Emcizumab is recombinant bispecific monoclonal antibody which simultaneously binds factor IXa and factor X, exerting the same function as factor VIII but not expected to be susceptible to neutralising antibodies. It is given as a weekly subcutaneous injection. It has not yet been filed for regulatory review in the US or EU.
A related commentary discusses this study. The results are extremely important for the haemophilia treatment community, which has battled the haemostatic calamity of factor VIII inhibitor formation with the same bypassing therapies for the past 30 years. Although the preferred treatment of the infrequent events of breakthrough bleeding during the administration of emicizumab is not clear, it is obvious that repeated high doses of activated prothrombin complex concentrate should be avoided. Similarly, how emicizumab prophylaxis will be integrated with current schedules for the induction of immune tolerance to factor VIII remains to be evaluated. In the meantime, weekly subcutaneous emicizumab prophylaxis appears to offer a marked reduction in bleeding rates and improvement in quality of life for this very challenging patient group. Additional studies are already in progress to determine the benefit of emicizumab prophylaxis in paediatric patients with haemophilia with inhibitors, and a study involving patients with haemophilia A without inhibitors is planned.