Azathioprine or 6-mercaptopurine for induction of remission in Crohn's disease

  • Review
  • Intervention

Authors


Abstract

Background

The results from controlled clinical trials investigating the efficacy of azathioprine and 6-mercaptopurine for the treatment of active Crohn's disease have been conflicting and controversial. An updated meta-analysis was performed to assess the effectiveness of these drugs for the induction of remission in active Crohn's disease.

Objectives

The primary objective was to determine the efficacy and safety of azathioprine and 6-mercaptopurine for induction of remission in active Crohn's disease.

Search methods

A literature search for relevant studies (inception to June 13, 2012) was performed using MEDLINE, EMBASE and the Cochrane Library. Review articles and conference proceedings were also searched to identify additional studies.

Selection criteria

Randomized controlled trials (RCTs) of oral azathioprine or 6-mercaptopurine compared to placebo or active therapy involving adult patients with active Crohn's disease were selected for inclusion.

Data collection and analysis

Data were extracted by two independent observers based on the intention-to-treat principle. Outcomes of interest included: clinical remission, clinical improvement, fistula improvement or healing, steroid sparing, adverse events, withdrawals due to adverse events and serious adverse events. We calculated the pooled relative risk (RR) and 95% confidence intervals (95% CI) for each outcome. The methodological quality of included studies was evaluated using the Cochrane risk of bias tool. The overall quality of the evidence supporting each outcome was assessed using the GRADE criteria.

Main results

Thirteen RCTs (n = 1211 patients) of azathioprine and 6-mercaptopurine therapy in adult patients were identified: nine included placebo comparators and six included active comparators. The majority of included studies were rated as low risk of bias. There was no statistically significant difference in clinical remission rates between azathioprine or 6-mercaptopurine and placebo. Forty-eight per cent (95/197) of patients receiving antimetabolites achieved remission compared to 37% (68/183) of placebo patients (5 studies, 380 patients; RR 1.23, 95% CI 0.97 to 1.55). There was no statistically significant difference in clinical improvement rates between azathioprine or 6-mercaptopurine and placebo. Forty-eight per cent (107/225) of patients receiving antimetabolites achieved clinical improvement or remission compared to 36% (75/209) of placebo patients (8 studies, 434 patients; RR 1.26, 95% CI 0.98 to 1.62). There was a statistically significant difference in steroid sparing (defined as prednisone dose < 10 mg/day while maintaining remission) between azathioprine and placebo. Sixty-four per cent (47/163) of azathioprine patients were able to reduce their prednisone dose to < 10 mg/day compared to 46% (32/70) of placebo patients (RR 1.34, 95% CI 1.02 to 1.77). GRADE analyses rated the overall quality of the evidence for the outcomes clinical remission, clinical improvement and steroid sparing as moderate due to sparse data. There was no statistically significant difference in withdrawals due to adverse events or serious adverse events between antimetabolites and placebo. Ten percent of patients in the antimetabolite group withdrew due to adverse events compared to 5% of placebo patients (8 studies, 510 patients; RR 1.70, 95% CI 0.94 to 3.08). Serious adverse events were reported in 14% of patients receiving azathioprine compared to 4% of placebo patients (2 studies, 216 patients; RR 2.57, 95% CI 0.92 to 7.13). Common adverse events reported in the placebo controlled studies included: allergic reactions. leukopenia, pancreatitis and nausea. Azathioprine was significantly inferior to infliximab for induction of steroid-free clinical remission. Thirty per cent (51/170) of azathioprine patients achieved steroid-free remission compared to 44% (75/169) of infliximab patients (1 study, 339 patients; RR 0.68, 95% CI 0.51 to 0.90). The combination of azathioprine and infliximab was significantly superior to infliximab alone for induction of steroid-free clinical remission. Sixty per cent (116/194) of patients in the combined azathioprine and infliximab group achieved steroid-free remission compared to 48% (91/189) of infliximab patients (2 studies, 383 patients; RR 1.23, 95% CI 1.02 to 1.47). Azathioprine or 6-mercaptopurine therapy was found to be no better at inducing steroid free clinical remission compared to methotrexate (RR 1.13, 95% CI 0.85 to 1.49) and 5-aminosalicylate or sulfasalazine (RR 1.24, 95% CI 0.80 to 1.91). There were no statistically significant differences in withdrawals due to adverse events between azathioprine or 6-mercaptopurine and methotrexate (RR 0.78, 95% CI 0.23 to 2.71); between azathioprine or 6-mercaptopurine and 5-aminosalicylate or sulfasalazine (RR 0.98, 95% CI 0.38 to 2.54); between azathioprine and infliximab (RR 1.47, 95% CI 0.96 to 2.23); or between the combination of azathioprine and infliximab and infliximab (RR 1.16, 95% CI 0.75 to 1.80). Common adverse events in the active comparator trials included nausea, abdominal pain, pyrexia and headache.

Authors' conclusions

Azathioprine and 6-mercaptopurine offer no advantage over placebo for induction of remission or clinical improvement in active Crohn's disease. Antimetaboilte therapy may allow patients to reduce steroid consumption. Adverse events were more common in patients receiving antimetabolites although differences with placebo were not statistically significant. Azathioprine therapy is inferior to infliximab for induction of steroid-free remission. However, the combination of azathioprine and infliximab was superior to infliximab alone for induction of steroid-free remission.

Résumé scientifique

L'azathioprine ou 6-mercaptopurine pour le déclenchement de la rémission dans la maladie de Crohn

Contexte

Les résultats d'essais cliniques contrôlés examinant l'efficacité de l'azathioprine et la 6-mercaptopurine pour le traitement de la maladie de Crohn active sont contradictoires et controversés. Une méta-analyse mise à jour a été réalisée afin d'évaluer l'efficacité de ces médicaments pour l'induction d'une rémission dans la maladie de Crohn active.

Objectifs

L'objectif principal était de déterminer l'efficacité et l'innocuité de l'azathioprine et la 6-mercaptopurine pour linduction de la rémission dans la maladie de Crohn active.

Stratégie de recherche documentaire

Une recherche de la littérature pour les études pertinentes (du début jusqu'au 13 juin 2012) a été effectuée dans MEDLINE, EMBASE et The Cochrane Library. Des articles de revue et les actes de conférence ont également fait l'objet de recherches afin d'identifier des études supplémentaires.

Critères de sélection

Les essais contrôlés randomisés (ECR) de l'azathioprine ou de la 6-mercaptopurine orale par rapport à un placebo ou à un traitement actif impliquant des patients adultes souffrant de la maladie de Crohn active ont été sélectionnés pour l'inclusion.

Recueil et analyse des données

DATA ont été extraites par deux observateurs indépendants en se basant sur le principe d'intention de traiter. Critères de jugement principaux incluaient : Une rémission clinique, une amélioration clinique, une amélioration de la fistule ou la guérison, l'épargne des corticostéroïdes, les événements indésirables, les arrêts prématurés en raison d'événements indésirables et les événements indésirables graves. Nous avons calculé le risque relatif (RR) combiné et des intervalles de confiance (IC) à 95 % pour chaque critère de jugement. La qualité méthodologique des études incluses a été évaluée en utilisant l'outil Cochrane de risque de biais. La qualité globale des preuves étayant chaque résultat a été évaluée selon les critères GRADE.

Résultats principaux

Treize ECR (n =1 211 patients) de traitement chez des patients adultes par l'azathioprine et la 6-mercaptopurine ont été identifiés : neuf incluaient des comparateurs placebos et six incluaient des comparateurs actifs. La majorité des études incluses ont été considérées comme présentant un faible risque de biais. Il n'y a aucune différence statistiquement significative en termes de taux de rémission clinique entre l'azathioprine ou la 6-mercaptopurine et un placebo. Quarante-huit pour cent (95/197) des patients prenant des antimétabolites ont atteint une rémission, contre 37 % (68/183) des patients sous placebo (5 études, 380 patients ; RR 1,23, IC à 95 % 0,97 à 1,55). Il n'y a aucune différence statistiquement significative en termes de taux d'amélioration clinique entre l'azathioprine ou la 6-mercaptopurine et un placebo. Quarante-huit pour cent (107/225) des patients prenant des antimétabolites présentaient une amélioration clinique ou une rémission comparé à 36 % (75/209) des patients sous placebo (8 études, 434 patients ; RR 1,26, IC à 95 % 0,98 à 1,62). Il y avait une différence statistiquement significative au niveau de l'épargne de stéroïdes (défini comme dose de prednisone < 10 mg/jour pendant le maintien de la rémission) entre l'azathioprine et un placebo. Soixante-quatre pour cent (47/163) des patients sous azathioprine pouvaient réduire leur dose de prednisone à < 10 mg/jour contre 46 % (32/70) des patients sous placebo (RR 1,34, IC à 95 % 1,02 à 1,77). Les analyses GRADE évaluaient la qualité globale des preuves pour les critères de jugement de rémission clinique, d'amélioration clinique et d'épargne de stéroïdes comme étant modérée en raison de l'éparpillement des données. Il n'y a aucune différence statistiquement significative en termes d'arrêts prématurés en raison d'événements indésirables ou des événements indésirables graves entre des antimétabolites et un placebo. Dix pour cent des patients dans le groupe des antimétabolites ont arrêté prématurément en raison d'événements indésirables par rapport à 5 % des patients sous placebo (8 études, 510 patients ; RR 1,70, IC à 95 % 0,94 à 3,08). Des événements indésirables graves ont été rapportés chez 14 % des patients recevant de l'azathioprine par rapport à 4 % des patients sous placebo (2 études, 216 patients ; RR 2,57, IC à 95 % 0,92 à 7,13). Les événements indésirables les plus couramment rapportés dans les études contrôlées par placebo inclus : des réactions allergiques. la leucopénie, la pancréatite et des nausées. L'azathioprine était significativement moins efficace que l'infliximab pour induire une rémission clinique sans corticostéroïdes. Trente pour cent (51/170) des patients sous azathioprine ont obtenu une rémission sans stéroïdes contre 44 % (75/169) des patients sous infliximab (1 étude, 339 patients ; RR 0,68, IC à 95 % 0,51 à 0,90). La combinaison de l'azathioprine et de l'infliximab était significativement supérieure à l'infliximab seul pour induire une rémission clinique sans corticostéroïdes. Soixante pour cent (116/194) des patients dans le groupe de l'azathioprine et de l'infliximab combinés ont obtenu une rémission sans stéroïdes contre 48 % (91/189) des patients sous infliximab (2 études, 383 patients ; RR 1,23, IC à 95 % 1,02 à 1,47). Le traitement par azathioprine ou 6-mercaptopurine ne sest pas révélée plus efficace pour induire une rémission clinique sans corticostéroïdes par rapport au méthotrexate (RR 1,13, IC à 95 % 0,85 à 1,49) et au 5-aminosalicylate ou à la sulfasalazine (RR 1,24, IC à 95 % 0,80 à 1,91). Il n'y avait aucune différence statistiquement significative dans les arrêts prématurés en raison d'événements indésirables entre l'azathioprine ou la 6-mercaptopurine et le méthotrexate (RR 0,78, IC à 95 % 0,23 à 2,71) ; entre l'azathioprine ou 6-mercaptopurine et au 5-aminosalicylate ou à la sulfasalazine (RR 0,98, IC à 95 % 0,38 à 2,54) ; entre l'azathioprine et de l'infliximab (RR de 1,47, IC à 95 % 0,96 à 2,23) ; ou entre la combinaison de l'azathioprine et de l'infliximab et l'infliximab (RR 1,16, IC à 95 % 0,75 à 1,80). Les événements indésirables les plus fréquents dans les essais comparateurs actifs incluaient des nausées, des douleurs abdominales, une fièvre et des maux de tête.

Conclusions des auteurs

L'azathioprine et la 6-mercaptopurine ne présentent aucun avantage par rapport au placebo pour l'induction d'une rémission ou d'amélioration clinique dans la maladie de Crohn active. Un traitement par antimétabolites peut permettre aux patients de réduire leur consommation de corticostéroïdes. Les événements indésirables étaient plus fréquents chez les patients prenant des antimétabolites bien que les différences par rapport à un placebo n'étaient pas statistiquement significatives. L'azathioprine est moins efficace que l'infliximab pour induire une rémission sans corticostéroïdes. Cependant, la combinaison de l'azathioprine et de l'infliximab était supérieure à l'infliximab seul pour induire une rémission sans corticostéroïdes.

摘要

硫唑嘌呤和巯嘌呤治疗克罗恩病疗效的系统综述

研究背景

对照试验结果表明,人们对硫唑嘌呤和巯嘌呤治疗活动性克罗恩病的特异性疗效仍存有矛盾和争议。本文是对此类药物在缓解活动性克罗恩病疗效的系统综述进行更新。

研究目的

本研究的主要目的是评价硫唑嘌呤和巯嘌呤诱导克罗恩病缓解的疗效和安全性。

检索策略

文献检索数据库包括MEDLINE, EMBASE和Cochrane 图书馆,检索日期到2012年6月13日。同时检索综述类文献和会议报道以便发现其他的研究。

标准/纳入排除标准

纳入研究类型为RCT,干预措施为口服硫唑嘌呤或巯嘌呤,对照措施为安慰剂或有效对照,纳入患者为患有活动性克罗恩病者。

数据收集与分析

由2名研究者基于ITT分析独立地提取数据。研究的结局包括:临床缓解,临床表现为有效,瘘管缓解或愈合,激素减量,不良反应,因(严重)不良反应退出。对每一项结局计算其综合的RR值和95%可信区间。使用Cochrane推荐的risk of bias工具来评价纳入研究的方法学质量。使用GRADE系统来评价针对每一项结局所获得的证据。

主要结果

共计纳入13篇关于硫唑嘌呤和巯嘌呤治疗成人克罗恩病的研究(涉及1211人):其中9篇以安慰剂做对照,6篇为阳性对照。纳入的多数研究偏倚风险较低。在临床缓解率方面,硫唑嘌呤或巯嘌呤与安慰剂无统计学差异。48%(95/197)接受了硫唑嘌呤治疗的患者与37%(68/183)接受安慰剂治疗的患者获得了缓解,二者间无统计学差异 (源自5项研究,涉及380位患者; RR=1.23,95% CI 0.97 至1.55)。硫唑嘌呤与巯嘌呤相比,在临床好转率上无统计学差异。48%(107/225)的接受嘌呤抑制剂的患者获得了临床好转或缓解,与之相比安慰剂组好转或缓解率为36%(75/209)(源自8项研究,涉及434位患者;RR=1.26, 95% CI为0.98至1.62)。在激素未使用率方面,有显著的统计学差异(界定为强的松维持缓解剂量剂量<10mg/d)。64%使用硫唑嘌呤的患者可将强的松剂量减至<10mg/d,与之相比,安慰剂对照组为46% (32/70) (RR=1.34, 95% CI为1.02 至1.77)。以GRADE系统来评价证据质量,由于数据量有限,临床显效和停用激素两个结局为中等级别证据强度。免疫抑制剂组和安慰剂组在因(严重)不良事件退出方面没有明显的统计学差异。抗代谢药物组因不良事件退出率为10%,安慰剂组为5%(来自8项研究,涉及,510位患者,RR=1.70,95%CI为0.94至3.08)。硫唑嘌呤组严重不良事件报告率为14%,安慰剂组为4%(来自2项研究,涉及216位患者,RR=2.57,95%CI为0.92至7.13)。安慰剂对照组报告的一般不良事件包括:过敏反应, 白细胞减少症,胰腺炎,恶心。在诱导停用激素临床缓解方面,与英夫利昔单抗相比,硫唑嘌呤明显处于劣势。30%(51/170)的服用硫唑嘌呤的病人可以获得停用激素后的缓解,英夫利昔单抗组为44%(75/169) (源自1项研究,涉及339位患者,RR=0.68,95%CI为0.51至0.90)。在诱导停用激素后的临床缓解方面,联用硫唑嘌呤和英夫利昔单抗明显优于单用英夫利昔单抗。联合用药组缓解率为60%(116/194),英夫利昔单抗单独用药组缓解率为48%(91/189) (源自2项研究,涉及383位患者,RR=1.23,95%CI为1.02 至1.47)。在诱导停用激素后的临床缓解方面,没有发现硫唑嘌呤或巯嘌呤优于甲氨蝶呤(RR=1.13,95% CI为0.85至1.49)和5-氨基水杨酸或柳氮磺吡啶(RR=1.24,95%CI为0.80至1.91)。在因不良事件退出方面,以下各比较均无统计学差异:硫唑嘌呤或巯嘌呤与甲氨蝶呤(RR=0.78,95%CI为0.23至2.71),硫唑嘌呤或巯嘌呤与5-氨基水杨酸或柳氮磺吡啶(RR=0.98,95%CI为0.38至2.54),硫唑嘌呤与英夫利昔单抗(RR=1.47,95%CI为0.96至2.23),联用硫唑嘌呤加英夫利昔单抗与单用英夫利昔单抗(RR=1.16,95%CI为0.75至1.80)。在使用了药物治疗的试验中,常见的不良反应包括恶心,腹痛,发热和头痛。

作者结论

在诱导临床缓解和好转方面,硫唑嘌呤和巯嘌呤较安慰剂无优势。抗代谢治疗可能减少激素用量。尽管与安慰剂相比无统计学差异,但接受抗代谢治疗确实更易引发常见的不良反应。在诱导停用激素后的缓解方面,英夫利昔单抗由于硫唑嘌呤。然而,联用硫唑嘌呤和英夫利昔单抗优于单用英夫利昔单抗。

翻译注解

译者:冯硕(北京中医药大学循证医学中心);审校:梁宁。翻译由北京中医药大学循证医学中心组织与提供。

Plain language summary

Azathioprine or 6-mercaptopurine for the treatment of active Crohn's disease

Azathioprine and 6-mercaptopurine are immunosuppressive drugs that are thought to reduce inflammation by blocking the immune system. This review includes 13 randomized trials with a total of 1211 participants. Azathioprine and 6-mercaptopurine were found to be no more effective than placebo (fake medicine) for inducing remission in Crohn's disease. There is evidence to suggest that the combination of azathioprine and infliximab is superior to infliximab used as a single drug for induction of steroid-free remission in active Crohn's disease. Tumor necrosis factor (TNF) alpha blocking drugs like infliximab may provide an alternative treatment for patients who do not respond to corticosteroid or immunosuppressive drug treatment. Azathioprine and 6-mercaptopurine may reduce the need for steroid treatment and their use may therefore lead to a lower incidence of steroid related side effects. However, these drugs are slow acting and are associated with some rare, but serious side effects. In some patients they suppress formation of blood cells that fight off infection and allow blood to clot and they occasionally cause inflammation of the pancreas. These drugs have also been associated with an increased risk of lymphoma. For these reasons careful consideration needs to be given to the use of these drugs in patients with active Crohn's disease.

Résumé simplifié

L'azathioprine ou 6-mercaptopurine pour le traitement de la maladie de Crohn active

L'azathioprine et la 6-mercaptopurine sont des médicaments immunosuppresseurs qui sont supposés réduire l'inflammation en bloquant le système immunitaire. Cette revue comprend 13 essais randomisés totalisant 1 211 participants. L'azathioprine et la 6-mercaptopurine n'ont pas été démontrés comme étant plus efficaces que le placebo (médicament inactif) pour induire une rémission dans la maladie de Crohn. Il existe des preuves suggérant que la combinaison de l'azathioprine et de l'infliximab est supérieure à l'infliximab administré seul pour induire une rémission sans corticostéroïdes dans la maladie de Crohn active. Les médicaments bloquant le facteur de nécrose tumorale (TNF pour « Tumor Necrosis Factor ») alpha, tels que l'infliximab, pourrait fournir un traitement alternatif pour les patients qui ne répondent pas aux corticostéroïdes ou à un traitement immunosuppresseur. L'azathioprine et la 6-mercaptopurine pourrait réduire le recours à des corticostéroïdes et leur utilisation pourrait donc conduire à une incidence plus faible d'effets secondaires liés aux corticostéroïdes. Cependant, ces médicaments agissent lentement et sont associés à certains effets secondaires graves, mais rares. Chez certains patients, ils suppriment la formation de cellules sanguines qui combattent l'infection et créent les caillots sanguins et peuvent parfois entraîner une inflammation du pancréas. Ces médicaments ont également été associés à un risque accru de lymphome. Pour ces raisons, une attention particulière doit être accordée à l'utilisation de ces médicaments chez les patients atteints de maladie de Crohn active.

Notes de traduction

Traduit par: French Cochrane Centre 5th November, 2013
Traduction financée par: Pour la France : Minist�re de la Sant�. Pour le Canada : Instituts de recherche en sant� du Canada, minist�re de la Sant� du Qu�bec, Fonds de recherche de Qu�bec-Sant� et Institut national d'excellence en sant� et en services sociaux.

概要

硫唑嘌呤或巯嘌呤治疗克罗恩病疗效的系统综述

硫唑嘌呤和巯嘌呤是免疫抑制剂,其被视为通过抑制免疫系统而减轻炎症反应。本系统综述纳入13项随机对照试验,涉及1211名受试者。研究发现,在诱导克罗恩病缓解方面,硫唑嘌呤和巯嘌呤较安慰剂更有效。有证据显示,对活动性克罗恩病,在诱导缓解方面,联用硫唑嘌呤和英夫利昔单抗优于单用英夫利昔单抗。对皮质激素和免疫抑制剂无效的患者,可用肿瘤坏死因子-α拮抗剂,如英夫利昔单抗,来替代治疗。硫唑嘌呤和巯嘌呤可减少皮质激素的用量,因此可减轻应用皮质激素带来的副作用。然而这类药物起效较慢,并可能导致罕见而严重的不良反应。对某些患者,它们降低白细胞数目,易导致血栓形成,并且有偶发胰腺炎的可能。同时能增加患淋巴瘤的风险。因此对活动性克罗恩病的患者,需要仔细考量是否给予此类药物。

翻译注解

译者:冯硕(北京中医药大学循证医学中心);审校:梁宁。翻译由北京中医药大学循证医学中心组织与提供。

Laički sažetak

Azatioprin i 6-merkaptopurin za postizanje remisije u liječenju aktivne Crohnove bolesti

Azatioprin i 6-merkaptopurin su imunosupresivni lijekovi za koje se smatra da smanjuju upalu blokiranjem imunološkog sustava. Ovaj Cochrane sustavni pregled literature uključio je 13 randomiziranih kontroliranih pokusa u kojima je sudjelovalo ukupno 1211 ispitanika. Rezultati tih studija pokazuju da azatiprin i 6-merkaptopurin nisu bili bolji od placeba (lažnog lijeka) za postizanje remisije kad bolesnik ima aktivnu Crohnovu bolest. Dokazi pokazuju da je kombinacija azatioprina i infliksimaba bolja od samog infliksimaba za postizanje remisije u aktivnoj Crohnovoj bolesti, koja ne zahtijeva uzimanje steroida. Lijekovi koji blokiraju tumorski čimbenik nekroze (engl. tumor necrosis factor, TNF) kao što je infliksimab mogu biti druga mogućnost liječenja za pacijente koji ne odgovaraju na liječenje kortikosteroidima ili imunosupresivima. Azatioprin i 6-merkaptopurin mogu smanjiti potrebu za liječenjem steroiidma i njihova uporaba stoga može smanjiti učestalost nuspojava povezanih s uzimanjem steroida. Međutim, ti lijekovi sporo djeluju i povezani su s određenim rijetkim, ali ozbiljnim nuspojavama. U nekih pacijenata potiskuju stvaranje krvnih stanica koje se bore protiv infekcije, potiču zgrušavanje krvi i povremeno uzrokuju upalu gušterače (pankreatitis). Ti lijekovi su također povezani s povećanim rizikom od limfoma. Stoga je nužno detaljno razmotriti koje od tih lijekova koristiti u pacijenata s aktivnom Crohnovom bolesti.

Bilješke prijevoda

Hrvatski Cochrane
Prevela: Livia Puljak
Ovaj sažetak preveden je u okviru volonterskog projekta prevođenja Cochrane sažetaka. Uključite se u projekt i pomozite nam u prevođenju brojnih preostalih Cochrane sažetaka koji su još uvijek dostupni samo na engleskom jeziku. Kontakt: cochrane_croatia@mefst.hr

Summary of findings(Explanation)

Summary of findings for the main comparison. Azathioprine or 6-mercaptopurine versus placebo for induction of remission in Crohn's disease
  1. 1 Control group risk estimates come from control arm of meta-analysis, based on included trials
    2 Sparse data (163 events)
    3 Sparse data (182 events)
    4 Sparse data (8 events) and very wide confidence intervals
    5 Sparse data (79 events)
    6 Sparse data (41 events)

    7 Sparse data (19 events) and very wide confidence intervals

Azathioprine (AZA) or 6-mercaptopurine (6-MP) versus placebo for induction of remission in Crohn's disease
Patient or population: Patients with active Crohn's disease
Settings: Outpatients
Intervention: Azathioprine or 6-mercaptopurine versus placebo
OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
ControlAZA or 6-MP versus placebo
Clinical remission372 per 1000 1458 per 1000
(361 to 577)
RR 1.23
(0.97 to 1.55)
380
(5 studies)
⊕⊕⊕⊝
Moderate 2
 
Clinical remission or improvement359 per 1000 1452 per 1000
(352 to 582)
RR 1.26
(0.98 to 1.62)
434
(8 studies)
⊕⊕⊕⊝
Moderate 3
 
Fistula improvement or healing286 per 1000 1572 per 1000
(192 to 1696)
RR 2.00
(0.67 to 5.93)
18
(3 studies)
⊕⊕⊝⊝
Low 4
 
Steroid sparing effect457 per 1000 1612 per 1000
(466 to 809)
RR 1.34
(1.02 to 1.77)
143
(4 studies)
⊕⊕⊕⊝
Moderate 5
 
Withdrawals due to adverse events53 per 1000 190 per 1000
(50 to 163)

RR 1.70

(0.94 to 3.08)

510
(8 studies)
⊕⊕⊕⊝
Moderate 6
 
Serious Adverse events38 per 1000 1

98 per 1000

(35 to 271)

RR 2.57

(0.92 to 7.13)

216 (2 studies)⊕⊕⊝⊝
Low 7
 
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Summary of findings 2 Azathioprine versus infliximab for induction of remission in Crohn's disease

Summary of findings 2. Azathioprine versus infliximab for induction of remission in Crohn's disease
  1. 1 Control group risk estimates come from control arm of the study
    2 Sparse data (135 events)
    3 Sparse data (126 events)
    4 Sparse data (46 events)
    5 Sparse data (289 events)
    6 Sparse data (71 events)
    7 Sparse data (82 events)

Azathioprine (AZA) versus infliximab (IFX) for induction of remission in Crohn's disease
Patient or population: Patients with active Crohn's disease
Settings: Outpatients
Intervention: Azathioprine versus infliximab
OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
ControlAZA versus IFX
Clinical remission479 per 1000 1316 per 1000
(244 to 417)
RR 0.66
(0.51 to 0.87)
339
(1 study)
⊕⊕⊕⊝
Moderate 2
 
Clinical remission off steroids444 per 1000 1302 per 1000
(226 to 400)
RR 0.68
(0.51 to 0.90)
339
(1 study)
⊕⊕⊕⊝
Moderate 3
 
Mucosal healing283 per 1000 1156 per 1000
(93 to 266)
RR 0.55
(0.33 to 0.94)
214
(1 study)
⊕⊕⊕⊝
Moderate 4
 
Adverse events890 per 1000 1899 per 1000
(828 to 961)
RR 1.01
(0.93 to 1.08)

324

(1 study)

⊕⊕⊕⊝
Moderate 5
 
Withdrawals due to adverse events178 per 1000 1262 per 1000
(171 to 397)
RR 1.47
(0.96 to 2.23)
324
(1 study)
⊕⊕⊕⊝
Moderate 6
 
Serious adverse events239 per 1000 1268 per 1000
(184 to 387)
RR 1.12
(0.77 to 1.62)
324
(1 study)
⊕⊕⊕⊝
Moderate 7
 
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Summary of findings 3 Azathioprine + infliximab versus infliximab for induction of remission in Crohn's disease

Summary of findings 3. Azathioprine + infliximab versus infliximab for induction of remission in Crohn's disease
  1. 1 Control group risk estimates come from control arm of the study
    2 Sparse data (183 events)
    3 Sparse data (207 events)
    4 Sparse data (75 events)
    5 Sparse data (306 events)
    6 Sparse data (66 events)
    7 Sparse data (66 events)

Azathioprine (AZA) + infliximab (IFX) versus infliximab for induction of remission in Crohn's disease
Patient or population: Patients with active Crohn's disease
Settings: Outpatients
Intervention: Azathioprine + infliximab versus infliximab
OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
ControlAZA + IFX versus IFX
Clinical remission479 per 1000 1603 per 1000
(493 to 738)
RR 1.26
(1.03 to 1.54)
338
(1 study)
⊕⊕⊕⊝
Moderate 2
 
Clinical remission off steroids482 per 1000 1593 per 1000
(492 to 708)
RR 1.23
(1.02 to 1.47)
383
(2 studies)
⊕⊕⊕⊝
Moderate 3
 
Mucosal healing283 per 1000 1424 per 1000
(289 to 620)
RR 1.50
(1.02 to 2.19)
210
(1 study)
⊕⊕⊕⊝
Moderate 4
 
Adverse events890 per 1000 1899 per 1000
(837 to 970)
RR 1.01
(0.94 to 1.09)

342

(1 study)

⊕⊕⊕⊝
Moderate 5
 
Withdrawals due to adverse events178 per 1000 1206 per 1000
(134 to 320)
RR 1.16
(0.75 to 1.80)
342
(1 study)
⊕⊕⊕⊝
Moderate 6
 
Serious adverse events239 per 1000 1151 per 1000
(98 to 234)
RR 0.63
(0.41 to 0.98)
342
(1 study)
⊕⊕⊕⊝
Moderate 7
 
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Summary of findings 4 Azathioprine or 6-mercaptopurine versus methotrexate for induction of remission in Crohn's disease

Summary of findings 4. Azathioprine or 6-mercaptopurine versus methotrexate for induction of remission in Crohn's disease
  1. 1 Definition of clinical remission includes withdrawal from steroids.
    2 Control group risk estimates come from control arm of meta-analysis, based on included trials
    3 Sparse data (75 events)
    4 Two of the studies in the pooled analysis were rated as having a high risk of bias due to single-blind and open label designs
    5 Sparse data (27 events)
    6 The two studies in the pooled analysis were rated as having a high risk of bias due to single-blind and open label designs
    7 Sparse data (9 events) and very wide confidence intervals
    8 The two studies in the pooled analysis were rated as having a high risk of bias due to single-blind and open label designs

Azathioprine (AZA) or 6-mercaptopurine (6-MP) versus methotrexate (MTX) for induction of remission in Crohn's disease
Patient or population: Patients with active Crohn's disease
Settings: Outpatients
Intervention: Azathioprine or 6-mercaptopurine versus methotrexate
OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
ControlAZA or 6-MP versus MTX
Clinical remission 1500 per 1000 2565 per 1000
(425 to 1210)
RR 1.13
(0.85 to 1.49)
143
(3 studies)
⊕⊕⊝⊝
Low 3,4
 
Adverse events452 per 1000 2190 per 1000
(95 to 371)
RR 0.42
(0.21 to 0.82)
85
(2 studies)
⊕⊕⊝⊝
Low 5,6
 
Withdrawals due to adverse events119 per 1000 293 per 1000
(27 to 322)
RR 0.78
(0.23 to 2.71)
85
(2 studies)
⊕⊕⊕⊝
Very low 7,8
 
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Summary of findings 5 Azathioprine or 6-mercaptopurine versus 5-ASA or Sulfasalzine for induction of remission in Crohn's disease

Summary of findings 5. Azathioprine or 6-mercaptopurine versus 5-ASA or Sulfasalzine for induction of remission in Crohn's disease
  1. 1 Control group risk estimates come from control arm of study
    2 Sparse data (65 events)
    3 Maté-Jiménez 2000 was rated as having a high risk of bias due to open label design

    4 Unexplained heterogeneity

    5 Sparse data (15 events)

6-mercaptopurine (6-MP) versus 5-ASA for induction of remission in Crohn's disease
Patient or population: Patients with active Crohn's disease
Settings: Outpatients
Intervention: Azathioprine or 6-mercaptopurine versus 5-ASA
OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
Control6-MP versus 5-ASA
Clinical remission358 per 1000 1444 per 1000
(286 to 684)
RR 1.24 (0.80 to 1.91)156 (2 studies)⊕⊕⊝⊝
Very low 2,3,4
 
Withdrawals due to adverse events99 per 1000 197 per 1000 (38 to 251)RR 0.98 (0.38 to 2.54)156 (2 studies)⊕⊕⊝⊝
Low 3,5
 
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Background

6-Mercaptopurine (6-MP) (predominantly used as a chemotherapeutic agent) and its prodrug azathioprine (AZA) (an immune modifier agent) are purine analogues that competitively interfere with nucleic acid metabolism (Lennard 1992; Sahasranaman 2008). Consequently, both drugs reduce cell proliferation and have immune modulating properties. A deficiency of thiopurine methyltransferase (TPMT) enzyme appears to account for some dose- and metabolism-dependent toxicities such as leukopenia (and possible subsequent infection), thrombocytopenia, and malignancy (Weinshilboum 1980; Lennard 1983; Lennard 1989). Other toxicities such as rash, fever, arthralgias, pancreatitis, hepatitis, nausea, non-pancreatic abdominal pain and diarrhea appear to be hypersensitivity reactions (Sandborn 1996).

Azathioprine and 6-mercaptopurine have both been used to treat patients with active, steroid-refractory, and steroid-dependent inflammatory Crohn's disease, and patients with fistulizing Crohn's disease. Uncontrolled trials suggested efficacy for azathioprine (Brooke 1969; Avery-Jones 1966; Brooke 1970; Brown 1970; Drucker 1970; Fausa 1971; Rhodes 1971; Patterson 1971; Lennard-Jones 1972; Wallensten 1972; Javett 1972; Papp 1974; Brooke 1976; Nyman 1985; Korelitz 1985; Lemann 1990; Verhave 1990; Markowitz 1990; Perrault 1991; Shah 1991; O'Brien 1991; Korelitz 1993; Colonna 1994; Kessler 1995; D'Haens 1995; D'Haens 1997). Placebo controlled clinical trials have been performed in order to determine whether the results of these uncontrolled studies are valid (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Oren 1997; Reinisch 2008). The results from these controlled trials were conflicting and controversies regarding efficacy developed (Korelitz 1981; Lennard-Jones 1981). Much of the controversy centered on design flaws in some of the studies, which failed to take into account the prolonged time to onset of drug action (3 to 4 months minimum). Careful analysis of the controlled data, paying attention to duration of therapy, concomitant medications, and drug dosage, may reveal logical explanations for conflicting data and allow more valid conclusions to be reached regarding efficacy. There have also been studies comparing AZA or 6-MP to other active treatments or in combination with these treatments (Summers 1979; Oren 1997; Maté-Jiménez 2000; Ardizzone 2003; Colombel 2010). This systematic review is an update of a previously published Cochrane review (Prefontaine 2010).

Objectives

The primary objective was to assess the efficacy and safety of azathioprine and 6-mercaptopurine used for induction of remission in active Crohn's disease.

Methods

Criteria for considering studies for this review

Types of studies

Randomized placebo-controlled or active comparator trials were considered for inclusion.

Types of participants

Adult patients with Crohn's disease defined by conventional clinical, radiographic, and endoscopic criteria which was categorized as acute (active) inflammatory disease (CDAI > 150 points or Harvey-Bradshaw Index score > 7 points or presence of moderate to severe symptoms at the time of entry into the trial).

Types of interventions

Trials of oral azathioprine or 6-mercaptopurine therapy were considered for inclusion.

Types of outcome measures

The primary outcome was the proportion of patients with clinical remission as measured with a validated outcome (e.g. Crohn's Disease Activity Index score < 150 points or a Harvey-Bradshaw Index score < 3). The proportion of patients with clinical improvement or remission was a secondary outcome. The definitions of remission and improvement varied from study to study making exact comparisons across studies difficult. Therefore, the definition of improvement or remission used in each study was used for data extraction. Other outcomes of interest included fistula improvement or healing, steroid sparing effect, adverse events, withdrawals due to adverse events, and serious adverse events. Included studies were also reviewed for adverse events commonly associated with antimetabolites including: leukopenia, infection, thrombocytopenia, malignancy, rash, fever, arthralgias, pancreatitis, hepatitis, nausea, non-pancreatic abdominal pain, and diarrhea.

Search methods for identification of studies

Electronic searches

We searched MEDLINE (Ovid), EMBASE (Ovid), and the Cochrane Library from inception to June 13, 2012. Conference proceedings were also searched to identify additional studies.

MEDINE and EMBASE were searching using the following strategy:

1     exp Crohn disease/ or exp colon Crohn disease/ or crohn.mp.
2     (crohn's or crohn's disease).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword]
3     (inflammatory bowel disease or IBD).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword]
4     crohn's/
5     inflammatory bowel disease/
6     1 or 2 or 3 or 4 or 5
7     (anti-metabolite* or anti-metabolite* or antimetabolite*).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword]
8     antimetabolite/
9     (6-mercaptopurine or mercaptopurine or 6-MP or 6MP).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword]
10     (AZA or azathioprine).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword]
11     azathioprine.rn.
12     azathioprine/
13     or/7-12
14     6 and 13
15     limit 14 to (humans and (controlled clinical trial or randomized controlled trial))

The Cochrane Library was searched using the following strategy:

#1 crohn
#2 crohn's or crohn's disease
#3 inflammatory bowel disease or IBD
#4 MeSH descriptor Crohn Disease explode all trees
#5 MeSH descriptor Inflammatory Bowel Diseases explode all trees
#6 (#1 OR #2 OR #3 OR #4 OR #5)
#7 anti-metabolite* or anti-metabolite* or antimetabolite*
#8 MeSH descriptor Antimetabolites explode all trees
#9 6-mercaptopurine or mercaptopurine or 6-MP
#10 MeSH descriptor 6-Mercaptopurine explode all trees
#11 AZA or azathioprine
#12 MeSH descriptor Azathioprine explode all trees
#13 (#7 OR #8 OR #9 OR #10 OR #11 OR #12)
#14 (#6 AND #13)

Searching other resources

We also searched conference proceedings and reference lists to identify additional studies.

Data collection and analysis

Study Selection:

Potentially relevant articles were reviewed in an independent unblinded fashion by two authors (DJT and JKM) to determine if they met the criteria specified above. In crossover studies, only data from the first portion of the study were incorporated to avoid possible carry-over effects of medication into the second part of the study, and to make these studies more comparable to those not of a crossover design. All results were tabulated on an intention-to-treat basis. Reviewers rated each article as being eligible, ineligible, or not applicable to the current review. Any disagreement among reviewers was resolved by consensus. Trials published in abstract form only were not included unless full details of the protocol and results could be obtained from the authors.

Data Collection:

Eligible articles were reviewed in duplicate and the results of the primary research trials were abstracted. Data were then extracted onto specially designed data extraction forms.

We used the Cochrane risk of bias tool (Higgins 2011) to assess the methodological quality of the included studies. The following study characteristics were assessed:

  1. Randomization sequence generation;

  2. Allocation concealment;

  3. Blinding of participants, outcome assessors and investigators;

  4. Incomplete outcome reporting (i.e. there was an acceptable method of dealing with attrition);

  5. Selective outcome reporting (i.e. all outcomes described in the methods were included in the analysis); and

  6. Other potential sources of bias.

Based on these characteristics, studies were judged to have a high, low or unclear risk of bias.

We used the GRADE approach to assess the overall quality of evidence for the primary outcome and selected secondary outcomes of interest. Outcomes from pooling of randomized trials start as high quality evidence, but may be downgraded due to: (1) risk of bias, (2) indirectness of evidence, (3) inconsistency (unexplained heterogeneity), (4) imprecision (sparse data), and (5) reporting bias (publication bias). The overall quality of evidence for each outcome was determined after considering each of these elements, and categorized as high quality (i.e. further research is very unlikely to change our confidence in the estimate of effect); moderate quality (i.e. further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate); low quality (i.e. further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate); or very low quality (i.e. we are very uncertain about the estimate) (Guyatt 2008; Schünemann 2011).

Statistical Analysis:

Data were analyzed using Review Manager (RevMan 5). The relative risk (RR) and 95% confidence intervals (95% CI) were calculated for each dichotomous outcome. Data from individual trials were combined for meta-analysis if the interventions, patient groups and outcomes were sufficiently similar (determined by consensus). A fixed-effect model was used to pool data in the absence of heterogeneity. A random-effects model was used when significant heterogeneity was detected. Heterogeneity was assessed using the Chi2 test (a P value of 0.10 will be regarded as statistically significant). The l2 statistic was used to estimate the degree of heterogeneity. This measure describes the percentage of total variation across studies that results from heterogeneity rather than chance. A value of 25% is considered to indicate low heterogeneity, 50% moderate heterogeneity and 75% high heterogeneity (Higgins 2003). Sensitivity analyses were used to explore potential sources of heterogeneity.

Results

Description of studies

A literature search conducted on June 13, 2012 identified 664 records. Four additional studies were identified through searching of conference abstracts. After duplicates were removed, a total of 541 trials remained for review of titles and abstracts. Two authors (DJT and JKM) independently reviewed the titles and abstracts of these trials and 26 studies were selected for full text review (see Figure 1). Thirteen of these studies were excluded (See: Characteristics of excluded studies). Thirteen trials met the pre-defined inclusion criteria and were included in the review (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Oren 1997; Maté-Jiménez 2000; Ardizzone 2003; Mantzaris 2004; Reinisch 2008; Colombel 2010).

Figure 1.

Study flow diagram.

The 13 selected trials (n = 1211 patients) had a variety of designs: seven were exclusively concerned with therapy of active disease (Colombel 2010; Maté-Jiménez 2000; Rhodes 1971; Klein 1974; Present 1980; Ewe 1993; Reinisch 2008), and two trials had separate arms for patients with active and quiescent disease (Willoughby 1971; Summers 1979). Oren 1997 compared therapy with 6-mercaptopurine, methotrexate, or placebo for active disease and subsequently for quiescent disease (if the patient responded) without randomizing for maintenance of remission therapy. In three trials patients were treated with 6-mercaptopurine (Present 1980; Oren 1997; Maté-Jiménez 2000). All the other included studies treated patients with azathioprine. Azathioprine is rapidly converted to 6-mercaptopurine in vivo, and the clinical indications for using azathioprine and 6-mercaptopurine are similar so it was decided that these trials could be pooled for meta-analysis. The authors of the National Co-operative Crohn's Disease Study (Summers 1979) divided their study into three parts and compared azathioprine, prednisone, sulfasalazine and placebo. Part I phase one dealt with patients with active disease, while part I phase two examined the ability of these patients to maintain their remission. Part II patients entered the study in remission. This review deals only with part I phase one for remission and all of part I for adverse event data (Summers 1979). Candy 1995 was divided into two parts. The first part treated active disease and the second part enrolled those who had successfully completed part one and examined their ability to maintain remission. This review deals only with part one of the Candy study.

Six studies included active comparators (Summers 1979; Oren 1997; Maté-Jiménez 2000; Mantzaris 2004; Reinisch 2008; Colombel 2010). As described above, Oren 1997 compared 6-mercaptopurine to placebo or methotrexate; and Summers 1979 examined azathioprine, prednisone, sulfasalazine and placebo. Colombel 2010 had three treatment arms including azathioprine, infliximab and infliximab plus azathioprine. Patients were followed for induction at 30 weeks and maintenance of remission at week 50 (Colombel 2010). Mantzaris 2004 compared treatment with infliximab to the combination of infliximab and azathioprine for active disease. Patients who were successfully induced at six weeks were entered into a one year maintenance phase and were treated with either infliximab or azathioprine alone (Mantzaris 2004). Maté-Jiménez 2000 randomized patients to one of three treatments: 6-mercaptopurine, azathioprine or 5-aminosalicyclic acid. Patients were followed for induction of remission at 30 weeks and then for maintenance through 76 weeks. Reinisch 2008 had three different treatment arms: everolimus, azathioprine and placebo. This trial was stopped early (at seven months) due to lack of efficacy of everolimus.

All patients were symptomatic: some had an acute exacerbation of previously quiescent disease (Ewe 1993), other patients had chronic disease unresponsive to other therapy such as steroids (Willoughby 1971; Klein 1974; Ardizzone 2003; Colombel 2010; Maté-Jiménez 2000), and some (Rhodes 1971; Present 1980; Summers 1979; Candy 1995; Oren 1997; Reinisch 2008) were evaluated only on the severity of their symptoms at the time of randomization. The steroid sparing effect of therapy was a primary end point for some studies (Willoughby 1971; Ewe 1993; Present 1980; Klein 1974; Oren 1997), while others (Rhodes 1971; Candy 1995) were concerned only with clinical response and did not consider the effect of concurrent medications. For some trials steroid free remission was the endpoint considered (Colombel 2010; Maté-Jiménez 2000). The National Cooperative Crohn's Disease Study (Summers 1979) measured only clinical response and by design excluded concurrent therapy.

Remission was measured at various time points in the included studies. Remission was measured at 16 weeks in two studies (Ewe 1993; Klein 1974). Candy 1995 and Reinisch 2008 measured remission at 12 weeks. Oren 1997 measured remission every month. Mantzaris 2004 measured remission at six weeks. Rhodes 1971 and Present 1980 were cross-over trials and the remission data before crossing over were used. Rhodes 1971 measured remission at two months and Present 1980 measured remission at one year. Summers 1979 measured remission at 17 weeks. Colombel 2010 measured remission at 26 weeks. Willoughby 1971 reported remission at 24 weeks. Maté-Jiménez 2000 reported remission at 30 weeks.

Risk of bias in included studies

The risk of bias for the included studies is summarized in Figure 2. Overall the studies were of low risk of bias for most assessed items. All of the trials were described as randomized, however only four studies explained the method used for sequence generation (Present 1980; Ardizzone 2003; Reinisch 2008; Colombel 2010). Four trials were rated as low risk of bias for allocation concealment (Summers 1979; Present 1980; Reinisch 2008; Colombel 2010). The remaining studies did not explain methods used for allocation concealment and were rated as unclear for this item (Rhodes 1971; Willoughby 1971; Klein 1974; Ewe 1993; Candy 1995; Oren 1997; Maté-Jiménez 2000; Ardizzone 2003; Mantzaris 2004). Seven studies were rated as low risk for blinding (Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Candy 1995; Reinisch 2008; Colombel 2010). Ardizzone 2003 was single-blind (investigator) and was rated as high risk for blinding. Maté-Jiménez 2000 was rated as high risk of bias for blinding because it was open label. Blinding was not discussed in Mantzaris 2004 and this study was rated as unclear for this study. Three studies were described as double-blind but did not explain the methods used for blinding. These studies were rated as unclear for blinding (Rhodes 1971; Ewe 1993; Oren 1997). Nine studies were rated as low risk for incomplete outcome data (Willoughby 1971; Klein 1974; Ewe 1993 Candy 1995; Oren 1997; Maté-Jiménez 2000; Ardizzone 2003; Mantzaris 2004; Colombel 2010). Four studies were rated as unclear for incomplete outcome data (Rhodes 1971; Summers 1979; Present 1980; Reinisch 2008). Twelve studies reported all expected outcomes (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Oren 1997; Ardizzone 2003; Mantzaris 2004; Reinisch 2008; Colombel 2010). Maté-Jiménez 2000 reported some additional post hoc analyses and was rated as unclear for selective reporting. No additional items of concern were noted and all studies were rated as low risk for other sources of bias (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Oren 1997; Maté-Jiménez 2000; Ardizzone 2003; Mantzaris 2004; Reinisch 2008; Colombel 2010).

Figure 2.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Effects of interventions

See: Summary of findings for the main comparison Azathioprine or 6-mercaptopurine versus placebo for induction of remission in Crohn's disease; Summary of findings 2 Azathioprine versus infliximab for induction of remission in Crohn's disease; Summary of findings 3 Azathioprine + infliximab versus infliximab for induction of remission in Crohn's disease; Summary of findings 4 Azathioprine or 6-mercaptopurine versus methotrexate for induction of remission in Crohn's disease; Summary of findings 5 Azathioprine or 6-mercaptopurine versus 5-ASA or Sulfasalzine for induction of remission in Crohn's disease

Azathioprine or 6-Mercaptopurine versus Placebo

Five placebo-controlled studies (Summers 1979; Ewe 1993; Candy 1995; Oren 1997; Reinisch 2008) involving 380 patients reported clinical remission at 12 to 17 weeks as an outcome using validated outcome measures (i.e. CDAI < 150 or HBI < 3). The pooled analysis showed no statistically significant difference in remission rates between antimetabolites (azathioprine and 6-mercaptopurine) and placebo. Forty-eight per cent (95/197) of patients receiving antimetabolites achieved remission compared to 37% (68/183) of placebo patients (RR 1.23, 95% CI 0.97 to 1.55). No statistically significant heterogeneity was detected for this comparison (P = 0.35; I2 = 9%). A GRADE analysis indicated that the overall quality of the evidence for the primary outcome (clinical remission) was moderate due to sparse data (163 events, see Summary of findings table 1). Subgroup analysis showed no statistically significant difference in remission rates between azathioprine and placebo (4 studies, 322 patients) or 6-mercaptopurine and placebo (1 study, 58 patients). Fifty-two per cent (86/165) of azathioprine patients achieved remission compared to 40% (62/157) of placebo patients (RR 1.24, 95% CI 0.94 to 1.64). Twenty-eight per cent (9/32) of 6-mercaptopurine patients achieved remission compared to 23% (6/26) of placebo patients (RR 1.22, 95% CI 0.50 to 2.98).

Nine placebo-controlled studies (n = 506 patients) reported clinical remission or improvement as an outcome (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Oren 1997; Reinisch 2008). The pooled analysis showed a statistically significant difference in clinical remission or improvement rates between antimetabolites (azathioprine and 6-mercaptopurine) and placebo. Fifty-one per cent (133/261) of patients receiving antimetabolites achieved clinical remission or improvement compared to 33% (80/245) of placebo patients (RR 1.53, 95% CI 1.05 to 2.22). However, statistically significant heterogeneity was detected for this comparison (P = 0.006; I2 = 64%). Subgroup analysis showed no statistically significant difference in remission or improvement rates between azathioprine and placebo (7 studies, 376 patients) or between 6-mercaptopurine and placebo (2 studies, 130 patients). Fifty-one per cent (98/193) of azathioprine patients achieved remission compared to 38% (69/183) of placebo patients (RR 1.28, 95% CI 0.96 to 1.71). No statistically significant heterogeneity was detected for the azathioprine subgroup comparison (P = 0.17; I2 = 35%). Fifty-one per cent (35/68) of 6-mercaptopurine patients achieved remission compared to 18% (11/62) of placebo patients (RR 2.54, 95% CI 0.60 to 10.68). However, a large statistically significant amount of heterogeneity was detected for the 6-mercaptopurine subgroup comparison (P = 0.02; I2 = 82%). The heterogeneity appears to be a result of the inclusion of the Present 1980 study in the pooled analysis. The Present 1980 study was quite different than the other studies in the pooled analysis as it did not use a validated outcome measure (e.g. CDAI) and it measured clinical improvement at one year whereas the other studies measured clinical remission or improvement between 6 and 28 weeks. To investigate if this study was the source of the heterogeneity the analysis was repeated excluding this trial. The pooled analysis now included 8 studies involving 434 patients. No statistically significant heterogeneity was detected for the overall comparison (P = 0.26; I2 = 22%) and the difference between antimetabolites and placebo was no longer statistically significant. Forty-eight per cent (107/225) of patients receiving antimetabolites achieved clinical remission or improvement compared to 36% (75/209) of placebo patients (RR 1.26, 95% CI 0.98 to 1.62). A GRADE analysis indicated that the quality of evidence was moderate due to sparse data (182 events, see Summary of findings table 1).

Present 1980 reported that the mean time to response with 6-mercaptopurine therapy in active Crohn's disease was 3.1 months, and that 19% of patients who responded took more than 16 weeks to respond. We therefore investigated the effect of duration of therapy on response. When the active disease therapy data were analysed for the effect of duration of therapy (range 6 weeks to 12 months), the pooled risk ratio for response within 1 to 16 weeks was 1.08 (95% CI 0.83 to 1.40) and response with > 17 weeks was 1.59 (95% CI 1.05 to 2.41). These risk ratios are not significantly different from one another as the confidence intervals overlap. Thus no conclusion can be drawn with respect to the length of therapy.

Four placebo-controlled studies reported fistula response as an outcome (Rhodes 1971; Willoughby 1971; Klein 1974; Present 1980). Two trials (Ewe 1993; Summers 1979) reported no statistically significant difference in healing rates between placebo and therapy groups but did not include numerical data. Present 1980 reported the number of fistulae that responded rather than the number of patients with fistulae that responded, so their results could not be pooled for analysis. We defined fistula response as complete healing or decreased discharge. If a fistula developed during the study, it was included as "unhealed". The pooled analysis included 3 studies and 18 patients. There was no statistically significant difference in fistula response between azathioprine and placebo patients. Fifty-four per cent (6/11) of azathioprine patients had a fistula response compared to 29% (2/7) of placebo patients (RR 2.00, 95% CI 0.67 to 5.93). No statistically significant heterogeneity was detected for this comparison (P = 1.00, I2 = 0%). A GRADE analysis indicated that the overall quality of the evidence for this outcome was low due to serious imprecision (very sparse data - 8 events and wide confidence intervals).

The ability to reduce prednisone or prednisolone dose was an important outcome measure for some studies. It was defined as the ability to follow a pre-defined steroid tapering regimen, and the ability to reduce steroid dose to < 10 mg/day while maintaining remission. Five studies reported the reduction of steroid consumption as an outcome (Willoughby 1971; Klein 1974; Present 1980; Ewe 1993; Candy 1995). However, Present 1980 reported only cross-over results for this outcome and we decided that it should not be included in the pooled analysis. The pooled analysis (4 studies, 143 patients) showed a statistically significant steroid sparing effect favouring azathioprine over placebo. Sixty-four per cent (47/73) of patients receiving azathioprine were able to reduce their prednisone dose to < 10 mg/day compared to 46% (32/70) of placebo patients (RR 1.34, 95% CI 1.02 to 1.77). No statistically significant heterogeneity was detected for this comparison (P = 0.40; I2 = 0%). A GRADE analysis indicated that the overall quality of the evidence was moderate for this outcome due to sparse data. Present 1980 reported that during treatment with 6-mercaptopurine in 44 patients, steroids could be discontinued in 23 patients and reduced in five (28/44). In 39 placebo patients steroids could be discontinued in five and reduced in one (6/39). This difference was statistically significant (RR 4.14, 95% CI 1.92 to 8.93). Oren 1997 reported no statistically significant difference in steroid consumption or ability to taper steroids between 6-mercaptopurine and placebo (data not shown).

Commonly reported adverse events in the placebo-controlled studies included allergic reactions (consisting of fever or rash or both and arthritis), leukopenia, pancreatitis and nausea. One study involving 80 patients reported the proportion of patients who experienced at least one adverse event (Reinisch 2008). There was no statistically significant difference in the incidence of adverse events between azathioprine and placebo. Sixty-nine per cent of patients in the azathioprine group experienced at least one adverse event compared to 86% of placebo patients (RR 0.81, 95% CI 0.64 to 1.02). Eight placebo-controlled trials reported the proportion of patients who withdrew due to adverse events (Rhodes 1971; Willoughby 1971; Klein 1974; Summers 1979; Present 1980; Ewe 1993; Candy 1995; Reinisch 2008). The adverse events reported from Present 1980 include both arms of the cross-over since data from the individual arms were not reported. All other data from cross-over studies were reported from the period prior to cross-over. The adverse events from Willoughby 1971 include both an induction of remission for active disease arm and a maintenance of remission arm since data from the individual arms were not reported. Summers 1979 reported adverse events from each part of the trial and did not split part I in to its phases. Oren 1997 did not report adverse event data. The pooled analysis (8 studies, 510 patients) showed no statistically significant difference in withdrawal due to adverse events. Ten per cent (28/266) of patients receiving antimetabolites withdrew due to adverse events compared to 5% (13/244) of placebo patients (RR 1.70, 95% CI 0.94 to 3.08). No statistically significant heterogeneity was detected for this comparison (P = 0.68; I2 = 0%). A GRADE analysis indicated that the overall quality of the evidence for this outcome was moderate due to sparse data (41 events, See Summary of findings table 1). Two studies (Summers 1979; Reinisch 2008) including 216 patients reported the proportion of patients who experienced serious adverse events (Summers 1979; Reinisch 2008). The pooled analysis showed no statistically significant difference in serious adverse events between antimetabolites (azathioprine and 6-mercaptopurine) and placebo. Fourteen per cent (15/111) of patients in the antimetabolite group had a serious adverse event compared to 4% of placebo patients (RR 2.57, 95% CI 0.92 to 7.13). There was no statistically significant heterogeneity detected for this analysis (P = 0.44; I2 = 0%). A GRADE analysis indicated that the overall quality of the evidence for this outcome was low due to very sparse data (19 events) and very wide confidence intervals (See Summary of findings table 1).

Azathioprine versus Infliximab

Colombel 2010 was the only study that compared azathioprine with infliximab. Clinical remission was a secondary outcome in this study. Patients with active Crohn's disease (CDAI 220 to 450) were included in the study. Clinical remission rates were significantly higher in those randomized to receive infliximab compared to azathioprine. Thirty-two per cent (54/170) of azathioprine patients achieved clinical remission at week 26 compared to 48% (81/169) of infliximab patients (339 patients, RR 0.66, 95% CI 0.51 to 0.87). A GRADE analysis indicated that the quality of evidence was moderate due to sparse data (135 events, see Summary of findings 2). Steroid free remission was the primary outcome in the Colombel 2010 study. Significantly more infliximab patients than azathioprine patients were able to achieve steroid free remission. Thirty per cent of azathioprine patients (51/170) achieved steroid free remission at 26 weeks compared to 44% (75/169) of infliximab patients (339 patients, RR 0.68, 95% CI 0.51 to 0.90). A GRADE analysis indicated that the quality of evidence was moderate due to sparse data (126 events, see Summary of findings 2).

Colombel 2010 reported mucosal healing by colonoscopy as an outcome. Mucosal healing was defined as the absence of mucosal ulceration at week 26 in patients who had confirmed mucosal ulceration at baseline (Colombel 2010). Mucosal healing rates were significantly higher in those randomized to receive infliximab compared to azathioprine. Twenty-eight per cent (28/99) of infliximab patients had mucosal healing at week 26 compared to 16% (18/115) of azathioprine patients (RR 0.55, 95% CI 0.33 to 0.94). A GRADE analysis indicated that the overall quality of evidence was moderate due to sparse data (46 events, see Summary of findings 2).

Colombel 2010 reported adverse events through week 54 of their trial. There was no statistically significant difference in the incidence of adverse events. Eighty-nine per cent (144/161) of patients in the azathioprine group experienced at least one adverse event compared to 89% (145/163) of patients in the infliximab group (RR 1.01, 95% CI 0.93 to 1.08). Common adverse events included nausea, abdominal pain, pyrexia and headache. There was no statistically significant difference in withdrawal due to adverse events. Twenty-six per cent (42/161) of azathioprine patients withdrew from the study because of an adverse event compared to 18% (29/163) of infliximab patients (RR 1.47, 95% CI 0.96 to 2.23). There was no statistically significant difference in the incidence of serious adverse events. Twenty-seven per cent of azathioprine patients (43/161) experienced a serious adverse event compared to 24% (39/163) of infliximab patients (RR 1.12, 95% CI 0.77 to 1.62). The overall quality of the evidence supporting these outcomes was moderate due to sparse data (see Summary of findings 2).

Azathioprine and Infliximab versus Infliximab

Two studies compared the combination of azathioprine and infliximab to infliximab alone (Mantzaris 2004; Colombel 2010). There was a statistically significant difference in clinical remission favouring the combination of azathioprine and infliximab over infliximab alone, however only Colombel 2010 reported this outcome. Sixty per cent (102/169) of patients in the combination therapy group achieved clinical remission compared to 48% (81/169) of infliximab patients (338 patients, RR 1.26, 95% CI 1.03 to 1.54). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (183 events, See Summary of findings 3). Both studies (Colombel 2010; Mantzaris 2004) reported steroid-free clinical remission as an outcome. There was a statistically significant difference in steroid-free clinical remission favouring the combination of azathioprine and infliximab over infliximab alone. Sixty per cent (116/194) of patients in the combination therapy group achieved steroid-free clinical remission compared to 48% (91/189) of infliximab patients (383 patients, RR 1.23, 95% CI 1.02 to 1.47). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (207 events, See Summary of findings 3). Colombel 2010 reported a statistically significant difference in mucosal healing. After 26 weeks of therapy, 42% (47/111) of patients in the combination therapy group achieved mucosal healing compared to 28% (28/99) of patients in the infliximab group (RR 1.50, 95% CI 1.02 to 2.19). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (75 events, see Summary of findings 3).

Colombel 2010 reported no statistically significant difference in the incidence of adverse events. Ninety per cent (161/179) of patients in the combination therapy group experienced an adverse event compared to 89% (145/163) of infliximab patients (RR 1.01, 95% CI 0.94 to 1.09). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (306 events, see Summary of findings 3). There was no statistically significant difference in withdrawal due to adverse events. Twenty-one per cent (37/179) of patients in the combination therapy group withdrew due to adverse events compared to 18% (29/163) of infliximab patients (RR 1.16, 95% CI 0.75 to 1.80). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (66 events, see Summary of findings 3). There was a statistically significant difference in the incidence of serious adverse events. Fifteen per cent of patients in the combination therapy group (27/179) experienced a serious adverse event compared to 24% (39/163) of infliximab patients (RR 0.63, 95% CI 0.41 to 0.98). A GRADE analysis indicates that the overall quality of the evidence for this outcome was moderate due to sparse data (66 events, see Summary of findings 3).

Azathioprine or 6-Mercaptopurine versus Methotrexate

Two studies compared 6-MP to methotrexate (Oren 1997; Maté-Jiménez 2000). Oren 1997 used the Harvey-Bradshaw Index to evaluate disease activity. Those with a score of ≥ 7 were included in the study and remission was defined as a Harvey-Bradshaw score of ≤ 3 and no steroid use. Maté-Jiménez 2000 included patients with steroid dependent Crohn's disease, defined as the inability to taper steroids below 20 mg/day without presenting symptoms of active disease (e.g. CDAI > 200). Remission was defined as CDAI < 150 with normal orosomucoid serum concentrations after discontinuing steroids. Ardizzone 2003 compared azathioprine to methotrexate. Ardizzone 2003 enrolled patients with active Crohn's disease (CDAI ≥ 200) with the need for steroids. Ardizzone 2003 defined remission as CDAI ≤ 150 and the discontinuation of steroid treatment. A pooled analysis (3 studies, n = 143 patients) revealed no statistically significant advantage for azathioprine or 6-MP over methotrexate, with 60% (45/75) of patients in the antimetabolites group achieving steroid-free remission compared to 57% (39/68) of methotrexate patients (RR 1.13, 95% CI 0.85 to 1.49). No statistically significant heterogeneity was detected for this comparison (P = 0.95; I2 = 0%). A GRADE analysis indicates that the overall quality of the evidence for this outcome was low due to sparse data (75 events) and a high risk of bias in two of the studies in the pooled analysis (See Summary of findings 4).

These studies provided little data on adverse events. Oren 1997 did not report adverse event data. Maté-Jiménez 2000 pooled adverse event data for Crohn's disease and ulcerative colitis, therefore only some of the adverse events were interpretable for Crohn's disease. Ardizzone 2003 provided adequate information with respect to adverse events. A pooled analysis (2 studies, 85 patients) showed that adverse events were significantly more likely in patients receiving methotrexate compared to azathioprine or 6-MP. Overall, adverse events occurred in 19% (8/43) of azathioprine or 6-MP patients compared to 45% (19/42) of methotrexate patients (RR 0.42, 95% CI 0.21 to 0.82). A GRADE analysis indicates that the overall quality of the evidence for this outcome was low due to sparse data (27 events) and a high risk of bias in two of the studies in the pooled analysis. There was no statistically significant difference in withdrawal due to adverse events. Adverse events leading to withdrawal occurred in 9% (4/43) of azathioprine or 6-MP patients compared to 12% (5/42) of methotrexate patients (RR 0.78, 95% CI 0.23 to 2.71). A GRADE analysis indicates that the overall quality of the evidence for this outcome was very low due to sparse data (9 events), very wide confidence intervals and a high risk of bias in two of the studies in the pooled analysis. No serious adverse events were reported in these studies.

Azathioprine or 6-Mercaptopurine versus 5-Aminosalicyclic Acid or Sulfasalazine

Maté-Jiménez 2000 compared 6-MP to 5-ASA. Summers 1979 compared azathioprine to sulfasalazine. A pooled analysis of two studies (n = 156) revealed no statistically significant advantage for azathioprine or 6-MP over 5-ASA or sulfasalazine. Forty-eight per cent (36/75) of patients in the antimetabolite group achieved remission compared to 36% (29/81) of patients who received 5-ASA or sulfasalazine (RR 1.24, 95% CI 0.80 to 1.91). There was statistically significant heterogeneity detected for this analysis (P = 0.03; I2 = 79%). A GRADE analysis indicates that the overall quality of the evidence for this outcome was very low due to sparse data (65 events), a high risk of bias in the Maté-Jiménez 2000 study, and unexplained heterogeneity (See Summary of findings 5). There was no statistically significant difference in withdrawals due to adverse events. Nine per cent of 6-MP patients (7/75) withdrew due to adverse events compared to 10% of patients (8/81) in the aminosalicylates group (156 patients, RR 0.98, 95% CI 0.38 to 2.54). There was no statistically significant heterogeneity detected for this comparison (P = 0.81; I2 = 0%). A GRADE analysis indicates that the overall quality of the evidence for this outcome was low due to sparse data (15 events) and a high risk of bias in the Maté-Jiménez 2000 study. Maté-Jiménez 2000 did not report serious adverse events and neither of the studies reported the proportion of patients who experienced at least one adverse event (Summers 1979; Maté-Jiménez 2000). Summers 1979 reported serious adverse events as an outcome. There was no statistically significant difference in the incidence of serious adverse events. Seven per cent of patients in the 6-MP group experienced a serious adverse event compared to 0% of 5-ASA patients (RR 11.25, 95% CI 0.62 to 204.86).

Discussion

This updated review includes 13 randomized controlled trials (n = 1211 patients) which examined the efficacy of azathioprine or 6-mercaptopurine for inducing remission in Crohn's disease. These trials compared these antimetabolites to placebo and various active therapies including infliximab, methotrexate and 5-aminosalicylate. The definitions of remission and improvement varied from study to study making exact comparisons across studies difficult. Only 5 of 9 (Summers 1979; Ewe 1993; Candy 1995; Oren 1997; Reinisch 2008) placebo-controlled studies used generally accepted and validated criteria (either a Crohn's Disease Activity Index score < 150 points or a Harvey-Bradshaw Index score < 3 points) to define remission. The other four studies used subjective improvement or other non-validated outcome measures (Rhodes 1971; Willoughby 1971; Klein 1974; Present 1980). Azathioprine or 6-mercaptopurine therapy was found to be no better than placebo (5 studies, 380 patients, RR 1.23, 95% CI 0.97 to 1.55) for achieving clinical remission. When clinical remission or improvement is considered as an outcome there was no statistically significant difference between azathioprine or 6-mercaptopurine and placebo (434 patients, RR 1.26, 95% CI 0.98 to 1.62). These results suggest that azathioprine and 6-mercaptopurine offer no advantage over placebo for induction of remission or clinical improvement in active Crohn's disease. We believe that the methodological basis for these conclusions is sound. The quality of the individual trials was assessed using the Cochrane risk of bias tool and the possibility of bias was judged to be low for these studies. A GRADE analysis indicated that the overall quality of the evidence supporting these outcomes is moderate due to sparse data. These findings agree with a recent meta-analysis of immunosuppressives in inflammatory bowel disease (Khan 2011).

The ability to taper or discontinue corticosteroids is an important outcome to consider when treating Crohn's disease. Four older trials (Candy 1995; Ewe 1993; Klein 1974; Willoughby 1971) reported steroid-sparing (e.g. final prednisone dose < 10 mg/day) as an outcome. A pooled analysis of these studies showed that azathioprine had a statistically significant steroid sparing effect compared to placebo (143 patients, RR 1.34, 95% CI 1.02 to 1.77). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was moderate. The role of combined antimetabolite and steroid therapy in active disease has been controversial. The National Cooperative Crohn's Disease Study (Summers 1979) failed to show a statistically significant benefit for azathioprine monotherapy and has been criticised for not allowing concurrent steroid therapy during the lag period before azathioprine could act, and for not allowing sufficient time to assess the response to azathioprine (Korelitz 1981). Combination therapy with azathioprine and steroids may lead to a higher response rate with less steroid use.

More recent trials comparing antimetabolites to other active therapies reported steroid-free clinical remission as an outcome (Ardizzone 2003; Colombel 2010; Mantzaris 2004; Maté-Jiménez 2000; Oren 1997; Reinisch 2008). 6-Mercaptopurine was found to be significantly better at inducing steroid-free remission than 5-aminosalicyclates (23 patients, RR 6.56, 95% CI 1.06 to 40.46). However, this result should be interpreted with caution due to the small number of patients included in the analysis and the poor methodological quality of the Maté-Jiménez 2000 study. The overall quality of the evidence was rated as very low using the GRADE approach due to risk of bias, imprecision and inconsistency. The Oren 1997 study is not adequate to determine the relative benefits of 6-mercaptopurine versus methotrexate. The sample size was small, both drugs were probably under-dosed (6-mercaptopurine 50 mg/day and methotrexate 12.5 mg/week orally), and neither drug was reported to be superior to placebo. A trial comparing oral 6-mercaptopurine 1.5 mg/kg/d or azathioprine 2 to 3 mg/kg/d with parenteral methotrexate 25 mg/wk for chronic active Crohn's disease would be of interest. A pooled analysis including three studies found no statistically significant difference in steroid-free clinical remission between azathioprine or 6-mercaptopurine and methotrexate (143 patients, RR 1.13, 95% CI 0.85 to 1.49). However, the results of this pooled analysis need to be interpreted with caution due to the small number of patients included in the analysis and because of a high risk of bias in two of the studies in the pooled analysis (Maté-Jiménez 2000; Ardizzone 2003). Furthermore, none of the three studies in the pooled analysis were designed as formal non-inferiority studies. A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was low. Azathioprine and 6-mercaptopurine may be better choices as first line steroid sparing agents than methotrexate due to the propensity for adverse effects. A pooled analysis of two studies found that patients taking methotrexate were significantly more likely than patients taking azathioprine or 6-mercaptopurine to experience an adverse event (85 patients, RR 0.42, 95% CI 0.21 to 0.82). More high quality trials comparing azathioprine or 6-mercaptopurine with 5-aminosalicyclates or methotrexate are required to determine the true comparative efficacy and safety of these interventions.

Azathioprine was found to be significantly less effective than infliximab (339 patients, RR 0.66, 95% CI 0.51 to 0.87) for achieving clinical remission. The addition of azathioprine to infliximab significantly improved clinical remission rates (338 patients, RR 1.26, 95% CI 1.03 to 1.54) compared to azathioprine alone. The combination of azathioprine and infliximab was found to be significantly superior to infliximab alone (383 patients, RR 1.23, 95% CI1.02 to 1.47) for induction of steroid-free remission. Azathioprine was found to be significantly inferior to infliximab therapy (339 patients, RR 0.68, 95% CI 0.51 to 0.90) for induction of steroid-free remission. A GRADE analysis rated the overall quality of the evidence for this comparison as moderate. Colombel 2010 also reported mucosal healing as an outcome. Azathioprine was found to be significantly inferior to infliximab for mucosal healing (RR 0.55, 95% CI 0.33 to 0.94). The combination of azathioprine and infliximab was found to be significantly superior to infliximab alone for mucosal healing (RR 1.50, 95% CI 1.02 to 2.19). A GRADE analysis rated the overall quality of the evidence for these outcomes as moderate due to sparse data. More high quality trials comparing the combination of azathioprine with infliximab to infliximab alone are required to confirm the benefit of this combination.

The use of azathioprine for refractory fistulae was originally based on uncontrolled reports (Avery-Jones 1966; Brown 1970; Brooke 1970; Drucker 1970; Korelitz 1985). For three placebo controlled trials that reported numerical results (Rhodes 1971; Willoughby 1971; Klein 1974), azathioprine therapy was found to have no advantage over placebo for fistula healing (RR 2.00, 95% CI 0.67 to 5.93). However, this pooled analysis included only 18 patients and further research is necessary to determine if azathioprine provides a benefit for fistula healing. In the Present 1980 study, forty fistulae were observed in 36 patients, and 9/29 (31%) of fistulae closed completely during treatment with 6-mercaptopurine compared with 1/17 (6%) of fistulae which closed during treatment with placebo (these numbers represent overlapping patients, some who crossed over and some who did not). The Present 1980 data were not included in this systematic review because the data were reported as the number of fistulae closing, rather than the number of patients who had complete fistulae closure, and because the fistulae data were not presented in a way that made separation of the results from the first phase of the crossover study possible. The principle author of this study was contacted, and the original data are no longer available to address these issues. The results from two other studies which reported no significant effect (Summers 1979; Ewe 1993) also could not be included in the analysis because the fistulae data were not available. The lack of specific reporting on fistula response in these two trials may represent publication bias, as negative results were not reported. A randomized, double-blind, placebo-controlled trial of azathioprine designed to specifically address the question of efficacy in the subgroup of patients with fistulizing (perforating) Crohn's disease would be of interest.

The adverse effects of antimetabolite therapy are well recognised (Rhodes 1970; Rosman 1973; Haber 1986; Alstead 1990). Patients with Crohn's disease may have similar symptoms, so a comparison with a control group is useful to estimate the incidence of adverse effects attributable to therapy. Although there was no statistically significant difference in withdrawals due to adverse events, patients receiving azathioprine or 6-mercaptopurine may be more likely to withdraw due to an adverse event. Present 1989 reviewed their extensive experience with 6-mercaptopurine in 396 patients with inflammatory bowel disease and approximately 1800 patient-years of follow-up. Present 1989 reported a higher incidence of adverse reactions, presumably due to the longer duration of therapy and observation: significant infection (7.4%), pancreatitis (3.3%), neoplasm (3.1%), bone marrow suppression (2.0%), allergy (2.0%), and drug-induced hepatitis (0.3%). O'Brien 1991 reported an overall 10% incidence of adverse events sufficiently severe to justify stopping azathioprine or 6-mercaptopurine in their uncontrolled series of 78 patients with Crohn's disease. Two studies detailing the low toxicity of azathioprine with respect to bone marrow suppression and cancer risk in 755 patients with inflammatory bowel disease treated over 27 years have been reported (Connell 1993; Connell 1994). A follow-up report of patients with Crohn's disease treated with azathioprine or 6-mercaptopurine for up to 166 months did not show an increase in toxicity with long term use (Bouhnik 1996). More recent studies confirm the low risk of bone marrow suppression and cancer in IBD patients treated with azathioprine (Fraser 2002; Gisbert 2008). The time course for the occurrence of adverse events is variable. Allergic reactions and pancreatitis usually occur within a few weeks of beginning therapy, whereas bone marrow suppression, infection, and hepatitis may occur at any time. It was not possible to ascertain from the controlled trials reviewed for this meta-analysis what the time course was for the various forms of drug toxicity observed.

Four active comparator trials reported the proportion of patients who experienced at least one adverse event (Ardizzone 2003; Colombel 2010; Mantzaris 2004; Maté-Jiménez 2000). There was no statistically significant difference in adverse events rates between azathioprine and infliximab (RR 1.01, 95% CI 0.93 to 1.08). Furthermore, the combination of azathioprine and infliximab was found to have a similar rate of adverse event compared to infliximab alone (RR 1.01, 95% CI 0.94 to 1.09). Data on withdrawals due to adverse events were available for all of the comparisons. There were no statistically significant differences in withdrawals secondary to adverse events between azathioprine or 6-mercaptopurine and methotrexate (RR 0.78, 95% CI 0.23 to 2.71), between 6-mercaptopurine and aminosalicylates (RR 0.98, 95% CI 0.38 to 2.54) or between azathioprine and infliximab (RR 1.47, 95% CI 0.96 to 2.23). Moreover, combined therapy with infliximab and azathioprine did not cause increased withdrawals due to adverse events compared to infliximab alone (RR 1.16, 95% CI 0.75 to 1.80). The rate of serious adverse events was only reported in one study (Colombel 2010). Azathioprine was found to have similar serious adverse event rate compared to infliximab (RR 1.12, 95% CI 0.77 to 1.62). However, the addition of azathioprine to infliximab was found to significantly decrease the risk of a serious adverse event compared to infliximab alone (RR 0.63, 95% CI 0.41 to 0.98). GRADE analyses indicated that the overall quality of the evidence supporting these outcomes was low to moderate due to sparse data (Colombel 2010) or high risk of bias (Ardizzone 2003; Maté-Jiménez 2000). Further research is necessary to assess the long term safety of azathioprine and 6-mercaptopurine.

The above findings from the present meta-analysis highlight some of the problems with the use of azathioprine or 6-mercaptopurine in active Crohn's disease. First and foremost, our meta-analysis shows that antimetabolite therapy provides no benefit over placebo for induction of remission or clinical improvement in active Crohn's disease. This can be explained by the fact that in most of the included placebo-controlled trials except Summers 1979, all patients received steroids with their study intervention. Remission was induced by the steroids in these studies and not by azathioprine or 6-mercaptopurine. Azathioprine or 6-mercaptopurine may affect the pace at which steroids can be tapered. The time to steroid free remission was not assessed in this review. Thus, future research could consider including time to steroid-free remission as an outcome.

Furthermore, antimetabolite therapy may take a few months before onset of drug action (e.g. approximately three months, Present 1980; Sahasranaman 2008). To explore this we analyzed placebo-controlled trials by the time point when remission or clinical improvement was measured. Azathioprine or 6-mercaptopurine patients evaluated at 17 weeks or later were significantly more likely to be in remission than those taking placebo (RR 1.59, 95% CI 1.05 to 2.41). When remission or clinical improvement was measured before 17 weeks there was no statistically significant difference between antimetabolites and placebo (RR 1.08, 95% CI 0.83 to 1.40). These results suggest that a period of 17 weeks may be the minimum time period for an adequate trial of antimetabolite therapy. It had been postulated that the apparent long duration of therapy required to achieve benefit may be due to a requirement for equilibration of the active metabolite of the drug within tissues. It was also suggested that a high intravenous loading dose of the drug might overcome this problem (Sandborn 1995). However, a placebo-controlled trial of intravenous azathioprine loading (40 mg/kg over 36 hours) in patients with active steroid-refractory Crohn's disease receiving oral azathioprine did not show any benefit (Sandborn 1999).

Apart from potentially expediting induction of steroid-free remission, azathioprine may have a role as an adjunctive therapy to infliximab. This was illustrated by the superiority of the combination of infliximab and azathioprine to monotherapy with azathioprine or infliximab. Therapy with azathioprine and 6-mercaptopurine may help to prevent the development of antibodies to infliximab. The development of antibodies to infliximab has been associated with a loss of response to infliximab and the development of infusion reactions. An analysis of the ACCENT I data by Hanauer and colleagues found that patients who received immunosuppressive therapy (i.e. azathioprine, 6-mercaptopurine or methotrexate) in conjunction with infliximab had a significantly lower chance of developing antibodies to infliximab than patients who received infliximab monotherapy (Hanauer 2004). However, patients who were found to be positive for these antibodies were not less likely to have a clinical response or be in clinical remission at the end of the study. These results should be interpreted with caution as only 80 patients had positive antibodies (Hanauer 2004). Future trials should evaluate the interaction between antimetabolite therapy and infliximab with respect to antibody formation and efficacy.

Authors' conclusions

Implications for practice

Azathioprine and 6-mercaptopurine offer no advantage over placebo for induction of remission or clinical improvement in active Crohn's disease. Antimetabolite therapy may allow patients to reduce steroid consumption. There is evidence to suggest that the combination of azathioprine and infliximab is superior to infliximab monotherapy for induction of steroid-free remission in active Crohn's disease.

Implications for research

All of the studies reported in this analysis used clinical improvement or remission as the primary outcome. It would be of interest to know whether azathioprine or 6-mercaptopurine can induce mucosal healing. Preliminary uncontrolled observations have suggested that azathioprine does result in endoscopic healing of active Crohn's disease (Sandborn 1995; D'Haens 1997). Future studies should assess time to steroid-free remission as an outcome. The available data on fistulae closure in patients with Crohn's diease treated with azathioprine or 6-mercaptopurine is not adequate to make definite conclusions regarding efficacy. A randomized, double-blind, placebo-controlled trial of azathioprine therapy in patients with active fistulizing Crohn's disease would be of interest. More high quality trials comparing azathioprine or 6-mercaptopurine with 5-aminosalicyclates or methotrexate are required to determine the true comparative efficacy and safety of these interventions. Further research is required to confirm the superiority of combination of azathioprine and infliximab to infliximab monotherapy. Future research should also assess the efficacy and safety of the use of azathioprine with other biologics.

One method of reducing the systemic toxicity of mesalamine and corticosteroids has been to administer drugs topically via enema or delayed release oral capsule formulations. Two pharmacokinetic studies have demonstrated that administration of azathioprine as either a rectal foam enema or as an Eudragit S100 coated delayed release oral capsule results in marked decrease in systemic bioavailability of azathioprine (Van Os 1996; Zins 1997). The efficacy of these topical azathioprine formulations should be investigated in patients with Crohn's disease.

Acknowledgements

Funding for the IBD/FBD Review Group (September 1, 2010 - August 31, 2015) has been provided by the Canadian Institutes of Health Research (CIHR) Knowledge Translation Branch (CON - 105529) and the CIHR Institutes of Nutrition, Metabolism and Diabetes (INMD); and Infection and Immunity (III) and the Ontario Ministry of Health and Long Term Care (HLTC3968FL-2010-2235).

Miss Ila Stewart has provided support for the IBD/FBD Review Group through the Olive Stewart Fund.

Data and analyses

Download statistical data

Comparison 1. Azathioprine or 6-Mercaptopruine versus placebo
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Clinical remission5380Risk Ratio (M-H, Random, 95% CI)1.23 [0.97, 1.55]
1.1 Azathioprine4322Risk Ratio (M-H, Random, 95% CI)1.24 [0.94, 1.64]
1.2 6-Mercaptopurine158Risk Ratio (M-H, Random, 95% CI)1.22 [0.50, 2.98]
2 Clinical remission or improvement9506Risk Ratio (M-H, Random, 95% CI)1.53 [1.05, 2.22]
2.1 Azathioprine7376Risk Ratio (M-H, Random, 95% CI)1.28 [0.96, 1.71]
2.2 6-Mercaptopurine2130Risk Ratio (M-H, Random, 95% CI)2.54 [0.60, 10.68]
3 Clinical remission or improvement (sensitivity analysis)8434Risk Ratio (M-H, Random, 95% CI)1.26 [0.98, 1.62]
3.1 Azathioprine7376Risk Ratio (M-H, Random, 95% CI)1.28 [0.96, 1.71]
3.2 6-Mercaptopurine158Risk Ratio (M-H, Random, 95% CI)1.22 [0.50, 2.98]
4 Clinical remission or improvement by trial duration8434Risk Ratio (M-H, Random, 95% CI)1.26 [0.98, 1.62]
4.1 trials ≥17 weeks4216Risk Ratio (M-H, Random, 95% CI)1.59 [1.05, 2.41]
4.2 trials <17 weeks4218Risk Ratio (M-H, Random, 95% CI)1.08 [0.83, 1.40]
5 Fistula improvement or healing318Risk Ratio (M-H, Fixed, 95% CI)2.0 [0.67, 5.93]
6 Steroid sparing effect (final prednisone dose < 10 mg/day)4143Risk Ratio (M-H, Random, 95% CI)1.34 [1.02, 1.77]
7 Adverse events180Risk Ratio (M-H, Fixed, 95% CI)0.81 [0.64, 1.02]
8 Withdrawals due to adverse events8510Risk Ratio (M-H, Fixed, 95% CI)1.70 [0.94, 3.08]
9 Serious adverse events2216Risk Ratio (M-H, Fixed, 95% CI)2.57 [0.92, 7.13]
Analysis 1.1.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 1 Clinical remission.

Analysis 1.2.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 2 Clinical remission or improvement.

Analysis 1.3.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 3 Clinical remission or improvement (sensitivity analysis).

Analysis 1.4.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 4 Clinical remission or improvement by trial duration.

Analysis 1.5.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 5 Fistula improvement or healing.

Analysis 1.6.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 6 Steroid sparing effect (final prednisone dose < 10 mg/day).

Analysis 1.7.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 7 Adverse events.

Analysis 1.8.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 8 Withdrawals due to adverse events.

Analysis 1.9.

Comparison 1 Azathioprine or 6-Mercaptopruine versus placebo, Outcome 9 Serious adverse events.

Comparison 2. Azathioprine versus Infliximab
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Clinical remission through 26 weeks1339Risk Ratio (M-H, Fixed, 95% CI)0.66 [0.51, 0.87]
2 Steroid-free remission through 26 weeks1339Risk Ratio (M-H, Fixed, 95% CI)0.68 [0.51, 0.90]
3 Mucosal healing through 26 weeks1214Risk Ratio (M-H, Fixed, 95% CI)0.55 [0.33, 0.94]
4 Adverse events1324Risk Ratio (M-H, Fixed, 95% CI)1.01 [0.93, 1.08]
5 Withdrawals due to adverse events1324Risk Ratio (M-H, Fixed, 95% CI)1.47 [0.96, 2.23]
6 Serious adverse events through 54 weeks1324Risk Ratio (M-H, Fixed, 95% CI)1.12 [0.77, 1.62]
Analysis 2.1.

Comparison 2 Azathioprine versus Infliximab, Outcome 1 Clinical remission through 26 weeks.

Analysis 2.2.

Comparison 2 Azathioprine versus Infliximab, Outcome 2 Steroid-free remission through 26 weeks.

Analysis 2.3.

Comparison 2 Azathioprine versus Infliximab, Outcome 3 Mucosal healing through 26 weeks.

Analysis 2.4.

Comparison 2 Azathioprine versus Infliximab, Outcome 4 Adverse events.

Analysis 2.5.

Comparison 2 Azathioprine versus Infliximab, Outcome 5 Withdrawals due to adverse events.

Analysis 2.6.

Comparison 2 Azathioprine versus Infliximab, Outcome 6 Serious adverse events through 54 weeks.

Comparison 3. Azathioprine and Infliximab versus Infliximab
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Clinical remission1338Risk Ratio (M-H, Fixed, 95% CI)1.26 [1.03, 1.54]
2 Steroid-free clinical remission2383Risk Ratio (M-H, Fixed, 95% CI)1.23 [1.02, 1.47]
3 Mucosal healing through 26 weeks1210Risk Ratio (M-H, Fixed, 95% CI)1.50 [1.02, 2.19]
4 Adverse events1342Risk Ratio (M-H, Fixed, 95% CI)1.01 [0.94, 1.09]
5 Withdrawals due to adverse events1342Risk Ratio (M-H, Fixed, 95% CI)1.16 [0.75, 1.80]
6 Serious adverse events1342Risk Ratio (M-H, Fixed, 95% CI)0.63 [0.41, 0.98]
Analysis 3.1.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 1 Clinical remission.

Analysis 3.2.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 2 Steroid-free clinical remission.

Analysis 3.3.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 3 Mucosal healing through 26 weeks.

Analysis 3.4.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 4 Adverse events.

Analysis 3.5.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 5 Withdrawals due to adverse events.

Analysis 3.6.

Comparison 3 Azathioprine and Infliximab versus Infliximab, Outcome 6 Serious adverse events.

Comparison 4. Azathioprine or 6-Mercaptopurine versus Methotrexate
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Steroid-free remission3143Risk Ratio (M-H, Fixed, 95% CI)1.13 [0.85, 1.49]
2 Adverse events285Risk Ratio (M-H, Fixed, 95% CI)0.42 [0.21, 0.82]
3 Withdrawals due to adverse events285Risk Ratio (M-H, Fixed, 95% CI)0.78 [0.23, 2.71]
Analysis 4.1.

Comparison 4 Azathioprine or 6-Mercaptopurine versus Methotrexate, Outcome 1 Steroid-free remission.

Analysis 4.2.

Comparison 4 Azathioprine or 6-Mercaptopurine versus Methotrexate, Outcome 2 Adverse events.

Analysis 4.3.

Comparison 4 Azathioprine or 6-Mercaptopurine versus Methotrexate, Outcome 3 Withdrawals due to adverse events.

Comparison 5. Azathioprine or 6-Mercaptopurine versus 5-Aminosalicylic acid or Sulfasalazine
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Steroid-free clinical remission2156Risk Ratio (M-H, Fixed, 95% CI)1.24 [0.80, 1.91]
2 Withdrawals due to adverse events2156Risk Ratio (M-H, Fixed, 95% CI)0.98 [0.38, 2.54]
3 Serious adverse events1133Risk Ratio (M-H, Fixed, 95% CI)11.25 [0.62, 204.86]
Analysis 5.1.

Comparison 5 Azathioprine or 6-Mercaptopurine versus 5-Aminosalicylic acid or Sulfasalazine, Outcome 1 Steroid-free clinical remission.

Analysis 5.2.

Comparison 5 Azathioprine or 6-Mercaptopurine versus 5-Aminosalicylic acid or Sulfasalazine, Outcome 2 Withdrawals due to adverse events.

Analysis 5.3.

Comparison 5 Azathioprine or 6-Mercaptopurine versus 5-Aminosalicylic acid or Sulfasalazine, Outcome 3 Serious adverse events.

What's new

DateEventDescription
16 April 2013AmendedCorrection of minor typos

History

Protocol first published: Issue 4, 1997
Review first published: Issue 4, 1997

DateEventDescription
13 March 2013New search has been performedNew literature searches conducted on June 13, 2012. New studies added
13 March 2013New citation required and conclusions have changedSubstantively updated review with new conclusions and authors

Declarations of interest

Nilesh Chande has received fees for consultancy from Abbott and Ferring, fees for lectures from Abbott, travel expenses from Merck and has stock/stock options in Pfizer, Takeda, Glaxo Smith Kline, Proctor and Gamble and Johnson and Johnson. All of these financial activities are outside the submitted work. John MacDonald has received fees for consultancy from Tillotts Pharma AG. All of these financial activities are outside the submitted work. David Tsoulis has no known declarations of interest.

Sources of support

Internal sources

  • University of Calgary, Calgary, Alberta, Canada, Not specified.

External sources

  • No sources of support supplied

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Ardizzone 2003

Methods

Randomized, controlled trial with blinded investigators

Intention to treat

6 month trial; all patients given standard prednisolone dose at the beginning of the trial

ParticipantsPatients (18 to 75 years old) with confirmed Crohn's disease on steroids for ≥ 4 months in the last year and active (CDAI ≥ 200) disease at entry (N = 54)
InterventionsIntravenous methotrexate for 3 months then oral administration for 3 months (25 mg/week) (n = 27) or oral azathioprine for 6 months (2.5 mg/kg) (n = 27)
Outcomes

Primary: steroid free clinical remission

Secondary: decreased steroid use, decreased CDAI, CRP or ERS, closure of fistulae

Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskQuote: "randomized by a computer-generated list"
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
High risk

Quote: "investigator-blind"

Quote: "patients and Chief of the Institute (GBP), who supervised the randomization, were aware of the treatment"

Quote: "The principal investigator (SA), who was blinded to treatment assignment, evaluated the efficacy of treatment at each scheduled visit and at the end of the study, according to the information provided by other physicians in the investigation team (SB, GM, VB, EC), all of whom were also blinded and evaluated each patient’s clinical condition, computed the CDAI on the basis of patient diaries, recorded all the biochemical parameters considered in the study, and monitored compliance and toxicity"

Incomplete outcome data (attrition bias)
All outcomes
Low riskQuote: "No patients were lost to follow-up. Six patients (three in azathioprine and three in methotrexate group) discontinued treatment due to adverse events. Withdrawal from the trial medication was considered as a treatment failure"
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Candy 1995

MethodsRandomized, double-blind, placebo-controlled
Intention to treat
12 weeks induction with tapering prednisolone dose, Month 3-15, no prednisolone, maintenance with azathioprine
(N = 63)
ParticipantsPatients with active disease, CDAI > 150
InterventionsAzathioprine (2.5 mg/kg/day) (n = 33) versus placebo (n = 30). All patients received a tapering dose of prednisolone (1 mg/kg)
OutcomesRemission (CDAI <150) at 12 weeks and maintenance at 15 months
NotesUnknown 5ASA use during trial and unknown previous steroid use before trial
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "patients were presented with tablets of identical appearance"

Quote: "double blind"

Incomplete outcome data (attrition bias)
All outcomes
Low risk20/63 participants withdrew by week 12 (azathioprine = 9/33, placebo = 11/30); 47/63 withdrew by month 15 (azathioprine = 19/33, placebo = 28/30). Data were analyzed by intention to treat and the reasons for withdrawal were reported
Selective reporting (reporting bias)Low riskA priori outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Colombel 2010

Methods

Randomized, double-blind trial comparing azathioprine, infliximab or combination of both

Intention to treat

30 weeks with a 20 week blinded extension option given

Primary outcome reported at 26 weeks

(N = 508)

Participants

Adult patients (≥21 years old) with CDAI between 220 and 450

Exclusion criteria: short bowel syndrome, ostomy, symptomatic stricture, abscess, recent abdominal surgery, history of tuberculosis or other granulomatous infection, positive chest x-ray or tuberculin skin test, recent opportunistic infection, active hepatitis C or V or HIV infection, multiple sclerosis, cancer or homozygous/heterozygous mutation to thiopurine methyltransferase phenotype

InterventionsAzathioprine 2.5 mg/kg (n = 170) versus infliximab 5 mg/kg (n = 169) versus combination of azathioprine and infliximab (n = 169)
Outcomes

Primary outcome: steroid-free remission rate

Secondary outcomes: mucosal healing (measured at week 26 in those who had ulcers at baseline), rate of clinical remission, response, IBDQ scores, corticosteroid dose, change in CRP from baseline

Remission was defined as < 150 CDAI

Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskQuote: "Randomization was performed centrally with the use of an adaptive randomization procedure"
Allocation concealment (selection bias)Low riskQuote: "Randomization was performed centrally with the use of an adaptive randomization procedure"
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "double-blind"

Quote: "daily oral placebo"

Quote: "placebo infusions"

Incomplete outcome data (attrition bias)
All outcomes
Low risk190/508 were withdrawn in the first 30 weeks. 280 patients entered the extension trial. Patients lost to follow up were assumed to not be in remission
Selective reporting (reporting bias)Low riskAll expected outcomes were reported in either the report or appendices
Other biasLow riskThe study appears to be free of other sources of bias

Ewe 1993

MethodsRandomized, double-blind, placebo-controlled
Intention to treat
16 weeks
(N = 42)
ParticipantsPatients with active disease, CDAI > 150
InterventionsAzathioprine (2.5 mg/kg/day) (n = 21) versus placebo (n = 21). All patients started with 60 mg prednisolone daily, reduced weekly to: 40, 30, 25, 20, 15, 10 mg. If taper successful, maintained at 10 mg/day prednisolone for the remainder of the trial
OutcomesRemission (CDAI < 150) at 17 weeks. No data on fistulae
NotesSteroid sparing effect found: azathioprine group more likely to follow tapering schedule and reinstitution of prednisolone more frequent in control group
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described (Quote: "allocation to each group was double blinded")
Blinding (performance bias and detection bias)
All outcomes
Unclear riskQuote: "double blinded"
Incomplete outcome data (attrition bias)
All outcomes
Low riskQuote: "None of the patients dropped out during the course of the trial"
Selective reporting (reporting bias)Low riskThe primary outcome (remission) was reported, along with all lab values
Other biasLow riskThe study appears to be free of other sources of bias

Klein 1974

MethodsRandomized, double-blind, placebo-controlled
Cross-over design: only data prior to cross-over used
Intention to treat
17 weeks
(N = 26)
ParticipantsPatients with active disease unresponsive to other forms of medical management
InterventionsAzathioprine 3 mg/kg/day (n = 13) versus placebo (n = 13). Concomitant steroid therapy at discretion of attending physician, but a conscious effort was made to taper steroids
OutcomesRemission defined as a subjective sense of improvement
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "double-blind"

Quote: "control subjects took a similar amount of dummy tablets (placebo)"

Incomplete outcome data (attrition bias)
All outcomes
Low risk2/13 patients from each group were unable to complete the study. Reasons for withdrawal were given
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Mantzaris 2004

MethodsRandomized controlled trial (N = 47) comparing infliximab alone (n = 20) to infliximab and azathioprine (n = 25) for induction phase (6 weeks). Patients who were successfully induced were entered into the maintenance phase and were treated with infliximab (5 mg/kg) every eight weeks (n = 16) or azathioprine alone (n = 20) for 1 year
ParticipantsAdult patients with active Crohn's disease (CDAI > 150) at entry
InterventionsInfliximab (5 mg/kg at week 0, 2, 6) or infliximab with azathioprine (2.5 mg/kg)
OutcomesInduction of remission at week 6 (CDAI < 150 and off steroids) and maintenance of remission at 1 year
NotesIt is not clear which group the missing two patients were assigned to
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Unclear riskNot described
Incomplete outcome data (attrition bias)
All outcomes
Low riskSeven patients withdrew, intention to treat followed
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Maté-Jiménez 2000

Methods

Randomized trial of 6-mercaptopurine, methotrexate and 5-aminosalicyclic acid in patients with inflammatory bowel disease

38 patients with Crohn's disease, 34 patients with ulcerative colitis

Induction for 30 weeks, followed for maintenance for 76 weeks (N = 38 with Crohn's)

Participants

Patients with steroid-dependent inflammatory bowel disease between 15 and 70 years old

Exclusion criteria: cardiac, hepatic or renal disease; bacterial infection; pregnancy, lactating or no use of reliable contraception, use of allopurinol, nonsteroidal anti-inflammatory drugs, tetracyclines or phenytoin; extensive surgery in the past

Interventions6-mercaptopurine (n = 16 with Crohn's), methotrexate (n = 15 with Crohn's) or 5-aminosalicyclic acid (n = 7 with Crohn's)
OutcomesPrimary outcome was clinical remission
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
High riskThe use of blinding was not described in the manuscript. We assume that blinding was not used
Incomplete outcome data (attrition bias)
All outcomes
Low risk24/72 patients withdrew in the first 30 weeks, reasons described, worst outcome assumed
Selective reporting (reporting bias)Unclear riskPrimary outcome was reported, as well as a number of other post hoc outcomes
Other biasLow riskThe study appears to be free of other sources of bias

Oren 1997

MethodsRandomized, double-blind, three arm study (6-mercaptopurine, methotrexate, placebo)
Intention to treat
9 months
(N = 84)
ParticipantsPatients with active disease, Harvey-Bradshaw Index ≥ 7
Interventions6-mercaptopurine 50 mg/day (n = 32) versus methotrexate 12.5 mg/week (n = 26) versus placebo (n = 26). 5-aminosalicylate and/or steroids continued at the discretion of the attending physician. Treating physicians were instructed to taper steroids and try to discontinue them within 2-3 months of entering the trial
OutcomesRemission defined as a Harvey-Bradshaw Index score ≤ 3 on the condition that the patient was not receiving steroids
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Unclear risk

Quote: "double blind"

Quote: "The investigators were blinded to treatment assignment"

Incomplete outcome data (attrition bias)
All outcomes
Low riskAttrition over the 9 month study were 13/26 for the methotrexate group, 9/32 for the 6-mercaptopurine group and 5/26 for the placebo. Data were analyzed by intention to treat and the method for dealing with missing data was outlined
Selective reporting (reporting bias)Low riskThe primary outcome (remission) was reported, along with all secondary outcomes
Other biasLow riskThe study appears to be free of other sources of bias

Present 1980

MethodsRandomized, double-blind, placebo-controlled
Crossover design, only data prior to cross over used for analysis of disease activity, data from both arms used to assess fistula effect, steroid sparing effect, and adverse effects
Intention to treat
52 weeks
(N = 83)
ParticipantsPatients with chronically active Crohn's disease, unresponsive to corticosteroids and sulfasalazine but surgery not imminent
Interventions6-mercaptopurine 1.5 mg/kg/day versus placebo
OutcomesImprovement in disease, healing of fistulae, steroid sparing effect
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskQuote: "random-number tables"
Allocation concealment (selection bias)Low riskQuote: "sealed envelopes"
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "Both tables...were identical in appearance and taste"

Quote: "patients and gastroenterologists were unaware of which treatment was being given"

Incomplete outcome data (attrition bias)
All outcomes
Unclear risk11/83 patients dropped out early. 8 from the 6-mercaptopurine group
Selective reporting (reporting bias)Low riskEffects on fistulas and steroid doses are explicitly discussed. Effect on signs and symptoms is discussed partially in the "Factors That Influenced the Response to 6-MP" section
Other biasLow riskSome problems with the cross-over protocol being followed, but no other issues

Reinisch 2008

Methods

Randomized, double blind , controlled trial

7 months

(N = 96)

Study stopped early because of lack of efficacy of everolimus

Participants

Adult patients (18 to 80 years old) with active Crohn's disease (CDAI 220 to 450)

Exclusion criteria listed in the study

InterventionsAzathioprine 2.5 mg/kg/day (n = 36), everolimus 6mg/day (n = 38) or placebo (n = 22)
OutcomesTreatment success and safety of everolimus
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskQuote: " randomization was performed using a validated interactive voice response randomization system that automated the random assignment of patient numbers to randomization numbers"
Allocation concealment (selection bias)Low riskQuote: "randomization was performed using a validated interactive voice response randomization system that automated the random assignment of patient numbers to randomization numbers"
Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: " A double-blind, double-dummy design was used to overcome the different forms of everolimus and azathioprine"
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskA large proportion of the patients initially enrolled (n = 144) appear not to be in remission after 3 months (n = 48). Furthermore, 54 patients withdrew from the study for various reasons. However, intention to treat was followed for the remaining 96 patients
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Rhodes 1971

MethodsRandomized, double-blind, placebo-controlled
Intention to treat
Crossover, only data from first arm of cross over used in analysis
8 weeks
(N = 12)
ParticipantsPatients with active Crohn's disease
InterventionsAzathioprine 4 mg/kg/day versus placebo for 10 days, then 2 mg/kg/day versus placebo for a total of 8 weeks of therapy
OutcomesResponse to treatment, fistulae improvement
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Unclear riskQuote: "double-blind"
Incomplete outcome data (attrition bias)
All outcomes
Unclear risk

2/16 withdrew

Quote: "two were withdrawn because of complications"

The group assignment was not provided for one of the withdrawals

Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Summers 1979

MethodsRandomized, double-blind, placebo-controlled
Intention to treat
17 weeks
N = 136
ParticipantsPatients with active disease, CDAI >150
InterventionsAzathioprine 2.5 mg/kg/day versus placebo
OutcomesRemission (CDAI <150) at 17 weeks
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Low riskCentralized randomization
Blinding (performance bias and detection bias)
All outcomes
Low riskQuote: "all prepared in uncoated tablets of identical external and internal appearance"
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskAttrition appears to be low but is not balanced across intervention groups
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Willoughby 1971

Methods

Randomized, double-blind trial

24 weeks

N = 22

Participants

Group 1: patients with active disease (subgroup included in this review) (n = 12)

Group 2: patients with disease controlled on prednisone (n = 10)

InterventionsAzathioprine 2 mg/kg or placebo; prednisone was tapered in both groups
OutcomesWithdrawal from trial because of deterioration in condition
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskNot described
Allocation concealment (selection bias)Unclear riskNot described
Blinding (performance bias and detection bias)
All outcomes
Low risk

Quote: "double blind"

Quote: "Only the pharmacist dispensing the tablets knew whether azathioprine or placebo had been selected for a given case"

Incomplete outcome data (attrition bias)
All outcomes
Low riskAll patients were included in the final analysis, withdrawal (as defined above) was the endpoint of the trial
Selective reporting (reporting bias)Low riskAll expected outcomes were reported
Other biasLow riskThe study appears to be free of other sources of bias

Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion
Chebli 2007Not a randomized controlled trial. Patients (N = 69) were given azathioprine after induction of remission with steroids and followed to see if they would maintain remission
Cosnes 2012All patients (N = 147) received azathioprine. Study compared accelerated step-care (steroids + early azathiorpine) to conventional step-care (steroids + azathioprine based on guidelines)
D'Haens 2008All patients (N = 133) received azathioprine. Study compared early combined immunosuppression (step-down: infliximab + azathioprine) to conventional step-up care (steroids for induction followed in sequence by azathioprine and infliximab)
Dejaco 2003Not a randomized trial. Patients (N = 52) with perianal fistulas received an antibiotic and azathioprine
Hinterleitner 1997Not a randomized trial. Patients (N = 9) with fistulas received cyclosporine, azathioprine and prednisolone
Ludwig 1999Not a randomized controlled trial. Patients (N = 89) were enrolled in an uncontrolled, investigator-blind study and received azathioprine therapy for 1 year, for induction of remission. Seventy-five per cent of patients were in remission at the end of 1 year
Lémann 2006All patients (N = 113) received AZA or 6-MP. Study compared efficacy of infliximab + azathioprine or 6-mercaptopurine versus placebo + azathioprine or 6-mercaptopurine
Mantzaris 2009Induction of remission was achieved by conventional steroids. Patients (N = 77) were randomized to receive azathioprine or budesonide to assess efficacy for maintenance of remission
Markowitz 2000A pediatric study. Patients (N = 55) were enrolled in a double-blind, placebo-controlled study and randomized to receive 6-mercaptopurine (1.5 mg/kg/day) and prednisone (40 mg/day) or placebo and prednisone (40 mg/day) for induction of remission. After 18 months, remission was induced in 89% of patients in both groups and was maintained in 91% of 6-MP patients compared to 53% of placebo patients. 6-MP also had a steroid-sparing effect compared to placebo
Miehsler 2001Not a randomized controlled trial. Forty-five patients were enrolled in this retrospective study comparing mycophenolate mofetil and azathioprine for induction of remission. All patients who completed the treatment achieved remission after 1 year. MMF had a faster steroid-sparing effect compared to AZA but had almost twice as many flare-ups as AZA
Neurath 1999The primary outcome for the review (clinical remission) was not reported. The primary outcome for the study was change in CDAI
Reinshagen 2007Randomized trial comparing standard dosing of azathioprine to adapted dosing of azathioprine
Watson 1974An abstract publication. Eleven patients enrolled into a randomised, double blind placebo controlled cross-over study of maintenance therapy, 1 year per arm Intervention: azathioprine 50 mg TID. Never published as a full paper, so unable to properly evaluate the methods and data. Preliminary analysis of the data showed no therapeutic advantage of azathioprine over placebo. No statistically significant change in objective disease score, but patients on azathioprine felt better, 1 patient in each group flared and required surgery