Clinical characteristics and outcomes of acquired hemophilia A before and after emicizumab approval in Japan

• Emicizumab effectively prevents bleeding in patients with acquired hemophilia A.

• Emicizumab may lead to shorter hospital stays, maintenance of activities of daily living, reduced costs, and improved prognosis.

Acquired hemophilia A (AHA) is a rare and potentially fatal bleeding disorder. Although bypassing agents effectively control active bleeding, their disadvantages, such as high cost and frequent administration, necessitate an agent that prevents recurrent bleeding events requiring bypassing agents. Emicizumab, a recombinant, humanized, bispecific monoclonal antibody with coagulation factor VIII-mimetic activity, was approved in Japan in 2022 for preventing bleeding in patients with AHA. However, owing to the rarity of the disease, real-world data on emicizumab use in AHA are scarce. Therefore, we aimed to assess the clinical characteristics and outcomes of 19 patients who were newly diagnosed with AHA before (N=12; non-emi-group) and after (N=7; emi-group) emicizumab approval in Japan. The median age, FVIII:C, and FVIII inhibitor titer were 81 versus 76 years, 1.0 versus 1.0%, and 43.75 versus 622 Bethesda units/mL, in the non-emi-group and the emi-group, respectively. Severe bleeding occurred in 14% of patients in the emi-group, compared with 58% of patients in the non-emi-group. Additionally, the doses of bypassing agents per patient were 43.4 versus 7, and the units of red blood cell transfusion per patient were 26.7 versus 4 in the non-emi-group and the emi-group, respectively. Their hospital stays were median 73.5 days and 44 days, respectively. All patients treated with emicizumab maintained their activities of daily living (ADLs) and experienced no side effects. This study suggests that emicizumab effectively prevents bleeding in patients with AHA. Moreover, emicizumab may lead to shorter hospital stays, maintained ADLs, reduced costs, and improved prognosis in patients with AHA.