The efficacy and safety of azithromycin in asthma: A systematic review

Abstract Azithromycin is a potential therapeutic choice for asthma control, which is a heterogeneous airway inflammatory disease. Because of variable findings, we intend to evaluate the therapeutic effect and safety of azithromycin in asthma. Databases, including PubMed, EMBASE, Cochrane, and CNKI until 31 December 2017, were searched to identify available randomised controlled trials regarding azithromycin treatment for asthma. We identified seven studies involving 1520 cases that met our criteria. The mean difference for lung function (FEV 1, FVC, PEF), symptom assessment (ACQ, AQLQ), airway inflammation, and risk ratios for adverse events were extracted. Chi‐square and I 2 tests were applied to evaluate the heterogeneity among the studies towards each index with a random effect model or a fixed effect model. Pooled analysis shows that azithromycin administration results in no significant improvement in FEV 1 (MD: 0.09, 95% CI −0.10 to 0.29, P = 0.36), PEF (MD: 11.76; 95% CI, −2.86 to 26.38, P = 0.11), total airway inflammatory cells (MD: −0.29; 95% CI, −1.38 to 0.80, P = 0.60), ACQ (MD: 0.05; 95% CI, −0.08 to 0.19, P = 0.44), and AQLQ (MD: 0.12; 95% CI, −0.02 to 0.26, P = 0.10). Moreover, no significant difference was detected in adverse events (Risk ratio 0.99; 95% CI, 0.82‐1.19, P = 0.90). These findings demonstrate no beneficial clinical outcome of azithromycin in asthma control, and we propose that further prospective cohorts are warranted.


| Data sources and search strategy
All of the literature reporting the effect of azithromycin in patients with asthma was systematically retrieved through the databases, including PubMed, EMBASE, and Cochrane Controlled Trials Register databases until 31 December 2017. The search keywords ("Azithromycin" AND "Asthma" OR "Bronchial asthma" OR "Allergic airway inflammation") were used to extract the related articles, without language restriction. The China National Knowledge Internet (CKNI) database was also searched from inception to December 2017 using equivalent Chinese terms. To identify other potentially eligible articles, studies were further searched manually by reviewing titles, abstracts, and full texts using EndNote X8 software. A manual search was also conducted on primary studies and review articles, and manufacturers' websites for trial information to avoid missing potential articles. This process was performed independently by two researchers.

| Inclusion and exclusion criteria
The inclusion criteria for considering studies of this systematic review were as follows: (a) all of the participants were definitely diagnosed as asthma; (b) studies were designed as randomised controlled trials; (c) azithromycin as the intervention treatment compared with placebo or azithromycin in combination with other therapies compared with other therapies alone; and (d) outcome reported lung function, airway inflammation, exacerbations, symptom control or adverse events. Studies were excluded if they had any of the following characteristics: (a) text without data about participant characteristics or outcome, such as guidelines, reviews, comments, correspondences, editorials, case reports; (b) studies were not performed in humans, or conducted in ex vivo cells or animals; (c) studies only analysed participants with a special occupation (eg, athletes and farmers). The eligible articles were judged and selected by two researchers independently.

| Data extraction
Two investigators independently abstracted the following information in eligible articles: study design, general characteristics of patients (sample size, age, number of female or male in each trial, country/area or gender), baseline of asthma severity, dosages and therapeutic process of azithromycin, the administration on asthma patients in placebo groups, duration of follow-up, and the primary and secondary outcome (forced vital capacity, FVC; forced expiratory volume in 1 second, FEV 1 ; peak expiratory flow, PEF; percentage of sputum eosinophils/neutrophils; asthma exacerbation rate; Asthma Quality of Life Questionnaire, AQLQ; Asthma Control Questionnaire, ACQ; and adverse events). Some data were calculated with available data by Review Manager (RevMan, version 5.3.0., Cochrane Collaboration, Oxford, UK), if they were not provided directly in texts. Any discrepancies were resolved by the third reviewer after assessing the original articles.

| Study quality assessment
The independent quality assessments for each of the RCTs were conducted according to the Cochrane Handbook for Systematic Reviews of Interventions by two authors. 9 A total of seven items (random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other bias) were applied for evaluating the risk of bias. The potential bias was graded as high, low, or unclear risk. Any divergence was settled by discussion with the third investigator.

| Statistical analysis
The changes in lung function (FEV 1 , FVC, PEF), symptom assessment (ACQ, AQLQ), airway inflammation, and adverse events rates were analysed in this systematic review. Chi-square and I 2 tests were used to evaluate the heterogeneity among the studies towards each index. P (χ 2 test) < 0.10 or I 2 ≥ 50% were considered statistical heterogeneity. A random effect model or fixed effect model was applied for meta-analysis with (P < 0.10, I 2 ≥ 50%) or without heterogeneity (P > 0.1, I 2 < 50%), respectively. The comparison of the outcome between the azithromycin and placebo was conducted using Review Manager 5.3 (Revman, The Cochrane Collaboration, Oxford, UK). P-values < 0.05 were considered statistically significant.
Kappa index was used to assess the consistency between the authors that performed this review; all values of that index were ≥ 0.75, indicating an acceptable consistency.

| Characteristics of included studies
Six-hundred-ninety studies were selected by searching PubMed, EMBASE, the Cochrane database, and CNKI, and 448 studies remained after removing duplicated texts. From the titles and abstracts, 419 studies were excluded because they were identified as guidelines, posters, comments, editorials or reviews, or involving ex vivo experiments, animal models or any other of the exclusion criteria. Twenty-nine studies were selected for the further full-text review, and finally, as shown in Figure 1, a total of seven studies with 1520 participants were selected for the systematic review and quantitative analysis. [10][11][12][13][14][15][16] All of the included studies were designed as randomised, double-blind, placebo-controlled clinical trials. Only one study was conducted in children, and the remaining six studies  as the usual care for asthma control; the ICS used in these studies included fluticasone or beclomethasone dipropionate. However, Hahn DL, Johnston SL, and Gibson PG have not provided details of the treatment in the placebo groups. 10,15,16 The characteristics of the studies are shown in Table 1.

| Risk of bias for included studies
We determined that six out of the seven studies were at low risk in both of random sequence generation and allocation concealment.
One study had not provided details for selection bias and was assessed as unclear risk. 14 Three studies stated that all of participants and investigators remained masked during the study, and were considered to be at low risk, 10,12,16 and no detailed information for performance bias and detection bias was provided in the other four studies. We considered all of the seven studies contributing data to be at low risk in attrition bias and reporting bias ( Table 2).

| Lung function changes
The seven included articles mentioned lung function changes after azithromycin or placebo treatment (Table S1). FEV 1 and PEF were analysed as follows.
DRS (percent fall of FEV 1 /mL) decreased from 2.75 ± 2.12 to 1.42 ± 1.54 (mean ± SD) in azithromycin-treated children (P = 0.02), and decreased (non-significantly) from 1.48 ± 1.75 at baseline to 1.01 ± 1.38 at the endpoint of the study in the placebo group (P = 0.21). As one of the secondary outcome, lung function changes were also assessed by Gibson et al, 16 who found no obvious improvement in FEV 1 after azithromycin administration compared with placebo.

| PEF variability
Three studies 13-15 evaluated PEF changes from baseline in adults.
The pooled analysis revealed no significant PEF improvement in azithromycin compared with the placebo group (MD: 11.76; 95% CI,  14 and Johnston (mean difference, 19.57; 95% CI, −6.81 to 45.94). 15 We performed leave-1out analyses to explore the sources of heterogeneity. By excluding the study of Johnston et al, heterogeneity was reduced to 0% (I 2 = 0%, P = 0.85) and with no significant difference in PEF (MD: 3.48; 95% CI, −13.35 to 20.31, P = 0.69), which further confirmed that the heterogeneity was mainly driven by the Johnston SL study.

| Airway inflammation
Airway inflammation is the distinct characteristic of asthma pathology. Three studies 11,14,16

| Adverse events
Two cohorts presented the comparison between azithromycin and placebo treatment in total adverse events. 13 | 1643 revealed no significant difference (Risk ratio 0.99; 95% CI, 0.82-1.19; P = 0.90) (Figure 7). Similarly, a meta-analysis result based on the three studies with 728 asthma patients, 13,15,16 indicated no significant between-group differences in serious adverse events (Risk ratio 0.64; 95% CI, 0.39-1.06; P = 0.08) (Figure 7). Overall, azithromycin used in asthma resulted in no obvious influence on adverse events by a meta-analysis (Risk ratio 0.89; 95% CI, 0.74-1.07; P = 0.22), which applied in a fixed effects models (heterogeneity I 2 = 0%, P = 0.45) (Figure 7). Moreover, there was no difference in study discontinuation due to adverse effects between the azithromycin and placebo group in the three studies cited above. As Hahn demonstrated, 12  In the included studies, there was more nausea and gastrointestinal and cardiac adverse events in the azithromycin group compared with the placebo. During one study, two patients were withdrawn due to The difference in treat-related adverse events level between azithromycin and placebo abnormal QTc prolongation, 16 which is a risk for cardiac arrhythmia and should be seriously considered in the clinical treatment.
Nevertheless, because of the varied heterogeneity of asthma, phenotypes, race, treatment duration, dose, and outcome measures, the effect of azithromycin in clinical trials about asthma patients are inconsistent. Non-eosinophilic asthma is seemly more responsive to azithromycin therapy than eosinophilic asthma, as Brusselle GG reported. 13 Add-on treatment with low dose azithromycin in patients with severe non-eosinophilic asthma (FeNO lower than the upper limit of normal and blood eosinophilia ≤ 200 ml −1 ) resulted in a significant reduction in the rate of severe exacerbations but showed no beneficial effect when subgroups of eosinophilic and non-eosinophilic asthma were analysed together. The underlying mechanism is unclear but could be attributed to combined actions of antibiotics and immunomodulation. By contrast, smokers with neutrophilic asthma did not indicate improved symptom control and lung function after azithromycin administration. 14 We suspect that the short treatment duration (12 weeks) is sufficient to get an effective dosage in this study. In an AMAZES clinical trial conducted in persistent asthma, azithromycin use was associated with reduced asthma exacerbations in both eosinophilic and non-eosinophilic asthma. 16 Moreover, these authors did not observe the decreased inflammatory cells in sputum, which was consistent with other studies, 11,14 indicating that there is no evidence of an antibacterial effect for azithromycin at this dose.
There are several limitations to this meta-analysis that should be (e) The dosage of azithromycin and period of conducting the study differed among studies, which might have contributed to the inconsistency; (f) We failed to identify unpublished studies that may alter the outcome; (g) We have not register this study on website for systematic reviews. Although there are several limitations of this study as listed above, we tried to address any study selection bias as described in Methods and we also ensured that the evaluation of each trial was consistently in line with the inclusion or exclusion criteria. Besides, we conducted this study strictly according to The Cochrane Handbook for Systematic Reviews of Interventions 5.1, which could minimised the bias as much as possible.

| CONCLUSION
In conclusion, this systematic review and meta-analysis has identified available randomised controlled clinical trials and investigated the efficacy and safety of azithromycin treatment for asthma patients.
We found no beneficial evidence for azithromycin for asthma patients in lung function, symptom control or asthma exacerbations, and careful consideration should be taken when using azithromycin.
Based on our findings, we propose that further prospective cohorts are warranted to assess the effectiveness and adverse events of azithromycin in asthma control.

ACKNOWLEDG EMENTS
This work was supported by the National Natural Science Foundation of China to TBP (No. 81700023).

CONFLI CT OF INTEREST
The authors declare no conflict of interest.