The U.S. Food and Drug Administration (FDA) has approved an expanded indication for the hemophilia treatment HYMPAVZI® (marstacimab-hncq) to now include people with hemophilia A or B. The new indication now included people ages 12 years and older with inhibitors—antibodies that develop against clotting factor treatments—and pediatric patients with hemophilia A and hemophilia B (ages 6 to 11 years) with or without inhibitors. These indications are for routine prophylaxis to prevent or reduce the frequency of bleeding episodes. HYMPAVZI was originally approved in 2024 for people ages 12 and older with hemophilia A or B without inhibitors.

Manufactured by Pfizer, marstacimab-hncq is a laboratory-engineered monoclonal antibody that targets an anticoagulant protein known as tissue factor pathway inhibitor (TFPI). It is administered subcutaneously once a week using a pen-like device. It works by blocking TFPI from performing the anticoagulant function that it naturally carries out in the human body. This effectively improves clotting and encourages coagulation. Watch the National Bleeding Disorders Foundation's video to learn more about how these treatments, also known as rebalancing agents, function within the clotting cascade. 

FDA’s expanded approval was based largely on interim results from the Phase 3 clinical trial known as BASIS KIDS. In it, children ages 6 to 17 years with hemophilia A or B with or without inhibitors who were treated once a week with marstacimab-hncq showed significant reductions in annual bleeding rates (ABRs). ABRs in the marstacimab-hncq-treated group were compared to historic models of patients who received traditional factor replacement therapy on-demand and prophylactically.

Source: Pfizer news release dated June 8, 2026