Coagulation potential of concomitant factor VIII administration in people with hemophilia A receiving emicizumab prophylaxis (CAGUYAMA study): a multicenter, open-label, nonrandomized clinical trial

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Background Emicizumab prophylaxis reduces bleeding in people with hemophilia A (PwHA). However, factor VIII (FVIII) is still required to manage breakthrough bleeding and surgical procedures. The optimal additional FVIII dose during such events remains unclear because of emicizumab's baseline hemostatic activity. Objectives To assess FVIII-induced changes in global coagulation potential in emicizumab-treated PwHA without inhibitors and to inform FVIII dosing during prophylaxis. Methods The multicenter CAGUYAMA study enrolled 100 PwHA (aged ≥4 years) receiving emicizumab at 13 centers in Japan. For eligible bleeding or surgical events, FVIII (standard or extended half-life) was administered at 30 ± 5 U/kg. Paired blood samples were obtained pre- and post-FVIII administration. The primary endpoint was change in clot waveform analysis (CWA)-adjusted maximum coagulation rate (Ad|min1|), expressed as IMCR% relative to pooled normal plasma and untreated severe HA plasma. Secondary endpoints included peak thrombin in thrombin generation assay (TGA), rotational thromboelastometry, clinical hemostasis, and safety. Anti-emicizumab antibodies were used in vitro to isolate FVIII effects. Results Thirty-two FVIII-treated events in 24 PwHA (15 bleeding events, 17 surgical events) were analyzed. CWA-IMCR% increased from 39.4% to 92.1% post-FVIII and from 3.2% to 78.6% under anti-emicizumab conditions. TGA peak thrombin increased from 249 to 348 nM (IMCR% 55.4% to 88.0%), and from 6.4% to 74.6% under anti-emicizumab conditions. All events achieved effective hemostasis. No thromboembolic events, thrombotic microangiopathy, or hypersensitivity reactions were reported. Conclusions FVIII administered at 30 ± 5 U/kg improved global coagulation parameters and achieved effective hemostasis without thrombotic complications, warranting evaluation during emicizumab prophylaxis.

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