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.