Evaluating the safety of emicizumab in patients with hemophilia A.

Introduction: Patients affected by hemophilia A often require frequent prophylactic and therapeutic self-infusion. For those who develop inhibitors, treatment options are limited and mortality is increased. Emicizumab, a bispecific antibody to Factors IXa and X that carries out the function of Factor VIII (FVIII), represents a novel therapeutic approach. Areas covered: We review the clinical trials and key laboratory assay research for emicizumab. Emicizumab reduced the annualized bleeding rate by 87% compared to placebo in patients with inhibitors. For patients without inhibitors, emicizumab reduced the annualized bleeding rate 96-97% compared to no prophylaxis and 68% compared to prior FVIII prophylaxis. Three patients developed a thrombotic microangiopathy (TMA) and two patients had thrombotic events while on emicizumab in combination with activated prothrombin complex concentration (aPCC) alone or concurrent with activated recombinant factor FVII (rFVIIa). Expert opinion: Emicizumab represents a much-needed alternative approach to managing Factor VIII deficiency, especially for those with inhibitors or limited ability to self-infuse. For patients with inhibitors, thrombotic complications including TMA, not seen with other bypassing agents, raises concern about the use of emicizumab in combination with aPCC and how patients who have breakthrough bleeding can be safely managed.