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- Patients and methods
Summary. Beriplex, a prothrombin complex concentrate (PCC), was administered to 42 patients requiring immediate reversal of their oral anticoagulant therapy. The dose administered was determined using the pretreatment International Normalized Ratio (INR). Blood samples were obtained before treatment and at 20, 60 and 120 min after treatment. The following investigations were performed on all samples – INR, clotting factors II, VII, IX and X, coagulation inhibitors protein C (PC) and antithrombin (AT), and other markers of disseminated intravascular coagulation, plasma fibrinogen, d-dimer and platelet count. Immediate reversal of the INR, the vitamin K-dependent clotting factors and PC was achieved in virtually all patients. Reduced AT levels were present in 18 patients before treatment. Further slight AT reductions occurred in four patients, but other associated abnormalities of haemostasis were observed in only one of the four patients. One patient with severe peripheral vascular disease, sepsis and renal and cardiac failure died of a thrombotic stroke following leg amputation, 48 h after receiving Beriplex. No other arterial and no venous thromboembolic events occurred within 7 d of treatment. Beriplex is effective in rapidly reversing the anticoagulant effects of warfarin, including PC deficiency, without inducing coagulation activation. Caution should continue to be exercised in the use of these products in patients with disseminated intravascular coagulation, sepsis or liver disease.
For patients receiving oral anticoagulant therapy, there are a number of clinical circumstances that necessitate rapid anticoagulant reversal. The most important indications are spontaneous life-threatening haemorrhage, trauma, particularly when associated with head injury, and prior to emergency surgery. We have previously demonstrated that, in situations in which complete and immediate correction of the oral anticoagulant effect is indicated, clotting factor concentrates are the only effective therapeutic option (Makris et al, 1997). However, a potential disadvantage of the use of these products is their associated thromboembolic risk (Lusher, 1991). For this reason, prothrombin complex concentrates (PCC) should be used with caution.
In this study we have evaluated the efficacy and safety of Beriplex P/N (Aventis, UK), a PCC, in 42 patients requiring immediate reversal of their oral anticoagulation with warfarin.
Patients and methods
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- Patients and methods
Forty-two warfarinized patients, 26 men and 42 women, aged 26–83 years (median 70 years) were studied. All were admitted into the Northern General or Royal Hallamshire Hospitals, Sheffield, during the period 1998–2001. A unified clinical and laboratory haematology service is provided for both hospitals. Each patient was considered by the admitting clinical team to require immediate reversal of his or her oral anticoagulant therapy. This was the only criterion for entry into the study. Patients were excluded if they were: (a) under 18 years of age; (b) pregnant; (c) had disseminated intravascular coagulation (DIC), evidenced by hypofibrinogenaemia, thrombocytopenia and elevated d-dimer; (d) known to be hypersensitive to plasma proteins; and (e) known to have hepatic dysfunction. Apart from the above exclusion criteria there was no selection of patients who were, wherever possible, entered consecutively into the study.
The clinical indications for oral anticoagulant reversal were: gastrointestinal haemorrhage (17), post head injury (5), subdural haematoma (5), miscellaneous spontaneous haemorrhage (5), emergency surgery (5), post trauma (2), miscellaneous causes (3), acute pancreatitis (1), acute abdomen and suspected intracranial haemorrhage (1).
Ethical approval for the study was obtained from the Central Sheffield University Hospitals (CSUH) Trust. Written, informed consent was obtained from all patients who were able to provide this. The Ethics Committee provided written approval to include those patients too ill to give prospective consent and who ultimately died before consenting.
The PCC used in the study was Beriplex P/N (Aventis, UK). Beriplex P/N 250 contains clotting factors II (320 IU), VII (170 IU), IX (250 IU) and X (380 IU). It also contains protein C (300 IU). Viral inactivation and elimination is by pasteurization and nanofiltration. The dose of Beriplex was based on the factor IX content of the product and was determined according to the pretreatment International Normalized Ratio (INR), as indicated in Table I.
Table I. Beriplex dosage and factor IX content determined by pretreatment Internationalized Normal Ratio (INR).
|INR||Dose (u/kg factor IX)|
Twenty patients received 25 u/kg, 12 patients received 35 u/kg and 10 patients received 50 u/kg Beriplex. One patient with mechanical heart valves and with an INR > 6·0 received 35 u/kg Beriplex on account of concerns expressed by the cardiologists in respect of valve-related thrombosis.
All patients received 2–5 mg of intravenous vitamin K given simultaneously with the Beriplex. Blood samples were taken before and 20, 60 and 120 min after treatment.
The following tests were performed on each sample: INR, clotting factors II, VII, IX and X, protein C (PC), antithrombin (AT), d-dimer, plasma fibrinogen, thrombin time and platelet count. Prothrombin times for INR determinations were performed using PT Fib HS-plus rabbit brain thromboplastin in combination with a Futura instrument (Instrumentation Laboratory Ltd, UK) and an instrument-specific International Sensitivity Index (ISI) and a locally derived mean normal prothrombin time. Standard one-stage clotting assays of factors II, VII and X were performed using PT Fib HS-plus. One-stage factor IX assays were performed using kaolin/platelet substitute (Diagnostic Reagents Ltd, Oxford, UK) with 5-min activation and 0·025 mol/l calcium chloride. All assays were determined with the ACL instrument using three dilutions of test plasma and human-deficient plasma (Precision Biologic, Canada). Assays were calibrated using three dilutions of a commercial reference material calibrated against World Health Organization (WHO) International Standards. Protein C was determined by chromogenic assay using Protac (Pentapharm, Switzerland) as an activator of PC. AT was determined by its' ability to inhibit bovine thrombin in the presence of excess heparin in a chromogenic assay (Dade-Behring, Milton Keynes, UK). Both AT and PC assays were calibrated using multiple dilutions of the 8th British Standard for Blood Coagulation Factors (NIBSC, Potters Bar, UK) and determined using a CA6000 coagulometer (Sysmex, Milton Keynes, UK). d-dimer was determined by agglutination of latex beads coated with antibody to d-dimer.
The Haemostasis Laboratory participates satisfactorily in the UK National External Quality Assessment Scheme (UKNEQAS) in respect of all investigations reported in this study.
When the study was initially conceived, the primary aims were to determine the rate of correction of the warfarin-induced coagulopathy and to establish whether there was associated coagulation activation and DIC. Following completion of the study, but before clinical events had been analysed, it was decided to include arterial and venous thrombovascular events. A decision was taken to report arterial thrombovascular events which occurred within 48 h of treatment with Beriplex and within 7 d for mortalities and venous thrombovascular events. The information was derived from inspection of the clinical records and also hospital discharge letters, death certificates and autopsy findings.
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- Patients and methods
In recent years the clinical indications for oral anticoagulant therapy have increased and, worldwide, many more patients are now receiving coumarins for both therapeutic and thromboprophylactic purposes. Despite the widespread adoption of INR monitoring for oral anticoagulant control, bleeding continues to be a serious complication of coumarin therapy. van der Meer et al (1993) reported 16·5 bleeding complications per 100 patient years, including 2·7 major bleeds per 100 patient years. More recently, following a prospective cohort study in Italian patients, Palareti et al (1996) reported 7·6 bleeding complications per 100 patient years, including 1·1 major bleeds per 100 patient years. Both studies observed an increased risk of bleeding with increasing INR and higher bleeding rates with increasing age. Intracranial haemorrhage is a particularly serious complication of oral anticoagulant therapy and occurs in 0·25–1·1% of patients per year (Butler & Tait, 1998).
It is therefore clear that there is a need for effective therapeutic regimens for oral anticoagulant reversal, particularly when clinical circumstances demand a rapid response. In this respect, we have recently reported the inadequacies of fresh-frozen plasma and have demonstrated the potential value of prothrombin complex concentrates (PCCs) (Makris et al, 1997).
A potential and important drawback to the routine use of PCCs for oral anticoagulant reversal is their known association with thromboembolism (Lusher, 1991). Kasper (1973) reported postoperative thrombophlebitis, thrombosis and pulmonary embolism in patients with haemophilia B following treatment with PCCs and, in 1975, a Task Force of the International Society for Thrombosis and Haemostasis (ISTH) reported the occurrence of DIC pulmonary embolism and acute myocardial infarction in haemophilia B patients receiving PCC treatment (Kasper, 1975). More recently, and before the introduction of high purity factor IX concentrates for the treatment of haemophilia B, the number of reports of PCC-related thrombosis has declined. It seems likely that this relates to improved quality of the products (Prowse & Cash, 1981).
The thrombogenicity of PCCs remains the subject of debate. There is evidence that this might relate to the presence of activated clotting factors in the products (Gray et al, 1995; Philippou et al, 1996), but imbalance between the procoagulant factors II and X on the one hand and inhibitors PC and PS on the other may be important (Köhler et al, 1990; Köhler, 1995).
In this study, and in order to detect clinically relevant coagulation activation, indicative of DIC, we elected to perform serial platelet counts, d-dimer, a specific marker of plasmin-mediated fibrinolysis of cross-linked fibrin, plasma fibrinogen and antithrombin assays.
A surprising observation was the occurrence of low AT activity, detected in 50% of patients in the study and before treatment with Beriplex. Acquired AT deficiency is usually a manifestation of hepatic dysfunction or DIC. On admission we did not perform detailed investigations of hepatic function, but it would seem highly unlikely that 50% of unselected warfarinized patients had clinically relevant liver disease. Although DIC is the more likely explanation for the low AT levels observed in this group of patients, the abnormal values were not accompanied by thrombocytopenia, hypofibrinogenaemia or elevated d-dimers, i.e. other laboratory markers of DIC. We are therefore unable to provide a convincing explanation for this observation.
Irrespective of the cause of the antithrombin deficiency, and apart from changes that occurred in a single patient, the administration of Beriplex was not accompanied by any further reductions in the AT levels, and plasma fibrinogen and d-dimer concentrations remained unchanged for the entire period of follow up.
In one patient, AT fell from a pretreatment level of 0·77 iu/ml to 0·45 iu/ml at 20 min. This was accompanied by a similar reduction in plasma fibrinogen but without an increase in d-dimer. We cannot exclude the possibility that these changes reflect genuine coagulation activation, but haemodilution is another possible explanation for the observed parallel reductions in AT and plasma fibrinogen levels as the patient was receiving intravenous hydroxyethyl starch at the time of testing.
Although treatment with 35 u/kg Beriplex resulted in a significant fall in the platelet count, the post-treatment counts remained within the normal range and were unaccompanied by other laboratory markers of DIC. Importantly, platelet counts remained unchanged in patients treated with the other two doses of the concentrate, including those treated with the higher dose of 50 u/kg. We were unable to detect evidence of coagulation activation following any of the three doses of Beriplex used in this study.
One possible explanation for the apparent lack of coagulation activation by this product is its' high concentration of protein C (PC). PC is a vitamin K-dependent protein and, consequently, all patients had reduced levels before anticoagulant reversal. Following treatment with Beriplex, normal PC levels were achieved at 20 min in 36 of the 42 patients. PC, through its' activated form APC, is an important natural anticoagulant with extensive anti-inflammatory properties. In the coagulation system, APC reduces thrombin and therefore fibrin formation by inactivating the clotting factors Va and VIIIa. Serial studies of PC and its' plasma inhibitor in patients with DIC provide compelling evidence for a major modulatory role for PC in DIC (Marlar et al, 1985). The possibility exists therefore that, in the patients described in this report, PCC-induced coagulation activation was reduced or suppressed by the simultaneous correction of the acquired PC deficiency.
Many of the patients described in this study were both elderly and extremely ill when admitted into hospital. This is reflected by the eight deaths which occurred shortly after admission. A thrombotic event was observed in only one of these. We cannot exclude the possibility that in this patient Beriplex was a contributory factor, but he also had severe arterial thrombovascular disease, necessitating emergency leg amputation, severe sepsis and both renal and cardiac failure. An autopsy, performed in three of the remaining seven patients, failed to demonstrate either arterial or venous thromboembolism.
We believe that these results provide good evidence that, in the patient group described here, rapid reversal of the haemostatic effects of warfarin was achieved by treatment with Beriplex and that this was unaccompanied by laboratory evidence of coagulation activation and, more importantly, clinical thrombovascular disease. Caution should continue to be exercised in the use of this and similar products in patients known to have DIC, liver disease or other risk factors for thrombovascular disease.
The increased use of prothrombin complex concentrates for the reversal of oral anticoagulation will depend not only on their reduced thrombogenic potential but also on their viral safety. Although this study was not designed to assess viral safety, this has improved immeasurably over the past 15 years and the risk of viral transmission by these products currently approaches zero.