Abstract Hemophilia A (HA) is an X-linked disorder characterized by a deficiency of factor VIII (FVIII). Approximately 30% of patients with severe HA (baseline FVIII levels < 1 IU/dL) develop antibodies that neutralize the activity of FVIIIs. Emicizumab, a bispecific monoclonal antibody that has FVIII mimetic activity, is effective at preventing bleeding in patients with HA and has become a standard prophylactic therapy for hemophilia patients with inhibitors. However, breakthrough bleeding and perioperative management still require additional bypassing agents, which increases the risk of thrombosis in these patients. This in vitro study compares the hemostatic effect of adding factor IX (FIX) to the plasma of HA patients on emicizumab prophylaxis with the addition of bypassing agents. Blood from 24 HA patients on emicizumab was collected, and plasma samples were spiked with increasing concentrations of recombinant factor VIIa (rFVIIa), activated prothrombin complex concentrate (aPCC), recombinant FIX (rFIX), and plasma-derived FIX (pdFIX). Thrombin generation (TG) was assessed using calibrated automated thrombography. Plasma emicizumab and FIX activity were measured. TG capacity improved significantly with increasing concentrations of rFVIIa (p < 0.0001), aPCC, rFIX, and pdFIX (p < 0.005). In contrast to high doses of aPCC and rFVIIa, TG parameters obtained with the addition of FIX did not cross the upper limit of normal physiologic ranges. Our data suggest a possible increased risk of thrombosis with higher concentrations of rFVIIa and aPCC, while adjunctive FIX therapy appears to be safe and effective in improving coagulation in HA patients with inhibitors on emicizumab prophylaxis. Future clinical trials are needed to confirm these results.
Janbain et al. (Thu,) studied this question.