The U.S. Food and Drug Administration has granted Priority Review to Pfizer’s supplemental Biologics License Application (sBLA) for HYMPAVZI® (marstacimab), seeking to expand its approved use to additional hemophilia patient populations with significant unmet medical needs.
The submission aims to extend the indication of HYMPAVZI to include patients aged six years and older with hemophilia A or B who have developed inhibitors, as well as pediatric patients aged six to 11 years with hemophilia A or B without inhibitors. If approved, HYMPAVZI would become the first non-factor prophylactic treatment available for children aged six to 11 years with hemophilia B.
HYMPAVZI is currently approved in the United States for patients aged 12 years and older with hemophilia A without factor VIII inhibitors or hemophilia B without factor IX inhibitors. The FDA has set a Prescription Drug User Fee Act (PDUFA) action date in the second quarter of 2026 for the expanded indication.
The therapy is designed to provide bleed protection through a once-weekly subcutaneous injection, requiring minimal preparation and no routine treatment-related laboratory monitoring. This approach is intended to address treatment challenges faced by patients with inhibitors and younger pediatric populations, where existing options are often limited or burdensome.
Hemophilia, typically diagnosed in early childhood, affects more than 800,000 people globally and is characterised by impaired blood clotting that can lead to recurrent bleeding, including joint bleeds that cause long-term damage. Children are particularly vulnerable due to ongoing bone and cartilage development. Inhibitors develop in approximately 20% of people with hemophilia A and about 3% of those with hemophilia B, rendering standard factor replacement therapies ineffective in many cases.
The FDA’s Priority Review designation is granted to therapies that may offer significant improvements over existing treatments or address conditions with limited therapeutic options, reducing the standard review timeline by four months. In addition, HYMPAVZI has received Breakthrough Therapy Designation for routine prophylaxis to prevent or reduce bleeding episodes in pediatric patients aged six to under 12 years with hemophilia B, both with and without inhibitors.
The sBLA submission for adults and adolescents is supported by efficacy and safety data from the Phase 3 BASIS trial, while the pediatric application is based on data from the Phase 3 BASIS KIDS trial. The use of HYMPAVZI for patients aged 12 years and older with hemophilia A or B with inhibitors is also currently under review by the European Medicines Agency.
HYMPAVZI is a monoclonal antibody discovered by Pfizer that targets tissue factor pathway inhibitor (TFPI), a natural regulator of blood clotting, rather than replacing missing clotting factors. By inhibiting TFPI, the therapy aims to restore balance between bleeding and clot formation.
The treatment has received regulatory approval in more than 40 countries and was the first anti-TFPI therapy approved in the U.S. and EU, as well as the first hemophilia medicine approved for administration via a pre-filled auto-injector pen.
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