A Study to Evaluate the Safest Dose Range for FEIBA in Hemophilia A Patients With Inhibitors on Emicizumab

Hemophilia A is a severe, life-long, genetic bleeding disorder characterized by a deficiency of factor VIII (FVIII), a crucial cofactor of the coagulation system. The mainstay of hemophilia treatment is factor replacement therapy with FVIII clotting factor concentrates (CFC) and these can be given episodically in response to bleeding or prophylactically to prevent bleeding. The main adverse effect of FVIII CFC is the development of neutralizing anti-drug antibodies termed inhibitors, and these render replacement therapy less effective if they are low titer inhibitors or completely ineffective if they are of the high titer variety. These so-called 'inhibitor patients' cannot rely on FVIII CFC for their treatment and are treated with other CFC called bypassing agents such as activated prothrombin complex concentrate (aPCC/Feiba). While these agents can be effective in some patients for prophylaxis, they are not as effective for bleed prevention as FVIII CFC for patients without inhibitors.Recently, emicizumab (Hemlibra, Roche), was developed and licensed for the prevention of bleeding in patients with hemophilia A with and without inhibitors. However, patients in the clinical trials for emicizumab have developed thrombotic adverse events and only patients who received doses of Feiba of \>100 IU/kg/24 hours for more than 24 hours developed thrombosis. As a result of the above data, recommendations have been to either avoid altogether in patients on emicizumab, or to be very cautious about using it to treat breakthrough bleeding. With this in mind, we propose to study the in vivo combination of Feiba in patients with inhibitors on emicizumab.