Real‐World Use of Emicizumab in Patients With Acquired Haemophilia A: An Interim Safety Analysis of a Large‐Scale Post‑Marketing Surveillance Study

INTRODUCTION: Acquired haemophilia A (AHA) is a rare autoimmune disorder where the development of autoantibodies to factor (F)VIII neutralise its function, leading to bleeding. Emicizumab has been approved for treating AHA in Japan. AIM: This post-marketing study was performed to primarily examine the use and safety of emicizumab, and indirectly assess effectiveness, for AHA patients in clinical practice in Japan. METHODS: This post-marketing surveillance study is being conducted in patients with AHA who receive emicizumab and immunosuppressive therapy (IST). For each patient, the observation period is from the first day of emicizumab to 4 weeks after the last administration, up to 24 months. The primary endpoint is adverse events (AEs). RESULTS: The first 51 patients who completed the survey were included in this interim analysis; 34 (66.7%) were male, and the median (range) age was 76.0 (33-91) years. Twenty-five (49.0%) patients experienced 63 AEs (45 serious). One thromboembolism occurred: cerebral infarction, unrelated to emicizumab. Nine (17.6%) patients died, due to infection (n = 4), haemorrhage (n = 3) and 'other' (n = 2), with no causal relationship with emicizumab in any case. Excluding the Week 1 emicizumab loading dose period, 8 (15.6%) patients received recombinant FVIIa while on emicizumab. All patients received IST from Day 1 (median initial prednisolone dose: 0.93 mg/kg). Median FVIII activity (one-stage assay) reached ∼60% in the patients who completed emicizumab treatment, and continued increasing after completion. CONCLUSIONS: This post-marketing study confirmed that emicizumab is well tolerated in patients with AHA, with no unexpected safety concerns. The benefit-risk profile of emicizumab remains favourable.