Pfizer Inc. (New York, NY) announced that the US FDA has accepted for filing a supplemental Biologics License Application (sBLA) and granted Priority Review for Hympavzi (marstacimab). The designation covers the treatment of individuals with hemophilia A or B without inhibitors who are 12 years of age or older and weigh at least 35 kg, as well as children aged 1 through 11 with hemophilia A or B with or without inhibitors. This regulatory milestone sets a six-month review clock for the application, significantly shortening the standard ten-month review period.
Hemophilia is a rare X-linked genetic disorder characterized by a deficiency in clotting factors (Factor VIII for hemophilia A and Factor IX for hemophilia B). Current prophylaxis and on-demand treatments still result in breakthrough bleeding and joint damage, particularly in pediatric populations and those without inhibitors. The disease landscape for pediatric patients with inhibitors is particularly challenging, as they often require frequent intravenous infusions of bypassing agents, a major area of unmet need.
Hympavzi is a human monoclonal antibody designed as a rebalancing therapy that targets the Kunitz 2 domain of Tissue Factor Pathway Inhibitor (TFPI). By inhibiting TFPI, the molecule allows for the generation of thrombin through the extrinsic pathway, effectively bypassing the need for Factor VIII or Factor IX. Hympavzi is administered as a subcutaneous injection, a delivery method intended to offer a less invasive alternative to traditional intravenous factor replacement therapies.
The sBLA submission is supported by data from two pivotal clinical trials. For the adolescent and adult population (12 years and older), the application includes data from the Phase III BASIS trial, which demonstrated a statistically significant reduction in annualized bleeding rates (ABR) compared to prior prophylaxis and on-demand regimens. For the pediatric population (ages 1 to 11), the submission is bolstered by results from the Phase III BASIS Kids trial, which evaluated the safety and efficacy of marstacimab in children with hemophilia A or B, with or without inhibitors.
The US FDA previously approved Hympavzi in October 2024 for the routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adult and adolescent patients with hemophilia A or B without inhibitors. If the sBLA is approved, Hympavzi would become the first and only TFPI inhibitor available for pediatric patients with hemophilia A or B with inhibitors. This Priority Review designation follows previous Orphan Drug and Fast Track designations granted by the FDA for the marstacimab development program.