Submission is to expand HYMPAVZI indication to the treatment of hemophilia A or B patients 6 years and older with inhibitors, and pediatric patients (ages 6 to 11) without inhibitors
Pfizer Inc. has announced that the US Food and Drug Administration has accepted and granted Priority Review to the company’s supplemental Biologics License Application for HYMPAVZI, also known as marstacimab. The application seeks to broaden the current approval to include people aged six years and older with hemophilia A or B who have inhibitors, as well as children between six and eleven years of age with hemophilia A or B who do not have inhibitors. In the United States, HYMPAVZI is already approved for patients aged twelve years and older with hemophilia A without factor VIII inhibitors or hemophilia B without factor IX inhibitors.
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The FDA has scheduled a target action date for its review decision in the second quarter of 2026 under the Prescription Drug User Fee Act. If the expanded indication is approved, HYMPAVZI could provide consistent bleed protection through a once weekly subcutaneous injection. The treatment is designed to be simple to administer, requires minimal preparation, and does not involve routine laboratory monitoring, which could ease the treatment burden for patients and caregivers managing complex forms of hemophilia.
Michael Vincent, MD, PhD, Chief Inflammation and Immunology Officer at Pfizer, noted that younger patients and those who develop inhibitors face particularly high unmet medical needs because inhibitors can block the effectiveness of traditional factor replacement therapies. He explained that data from the BASIS clinical trial program suggest HYMPAVZI could represent a meaningful advancement for patients who currently have limited or demanding treatment options. Vincent added that Pfizer is committed to continuing regulatory discussions to help bring this therapy to those who may benefit.
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Hemophilia is typically diagnosed early in life and affects more than 800000 people globally. The condition interferes with normal blood clotting and can lead to painful bleeding episodes, including internal joint bleeds that may cause lasting joint damage. Children are especially vulnerable because their joints and bones are still developing. Inhibitors develop in about twenty percent of people with hemophilia A and roughly three percent of those with hemophilia B, leaving many patients unable to rely on standard factor therapies.
Guy Young, MD, Director of the Hemostasis and Thrombosis Center at Children’s Hospital Los Angeles, emphasized that preventing bleeding in children aged six to eleven is critical to protecting joint health during growth. He stated that if approved, HYMPAVZI could help fill a major treatment gap, particularly for children with hemophilia B who currently lack effective non factor options.
Priority Review is granted by the FDA to therapies that may significantly improve treatment or address serious conditions with limited available options. This designation shortens the review timeline by four months. In addition, HYMPAVZI has received Breakthrough Therapy Designation for routine prophylaxis in pediatric patients aged six to under twelve with hemophilia B, with or without inhibitors. This designation is intended to speed development and review when early clinical evidence suggests substantial improvement over existing therapies.
The regulatory submission for adults and adolescents is supported by safety and efficacy data from the Phase 3 BASIS trial, while the pediatric submission relies on results from the Phase 3 BASIS KIDS study. HYMPAVZI is also under regulatory review in Europe for use in patients aged twelve and older with hemophilia A or B who have inhibitors.
HYMPAVZI was discovered by Pfizer scientists and works through a mechanism distinct from traditional factor replacement therapies. Instead of replacing clotting factors, it targets tissue factor pathway inhibitor, a natural regulator of blood clotting. By acting on this pathway, HYMPAVZI is designed to help restore balance between bleeding and clot formation. The therapy has already received approval in more than forty countries for eligible patients with hemophilia A or B without inhibitors and was the first anti TFPI treatment approved in both the US and European Union. It is also the first hemophilia therapy approved in these regions to be delivered using a pre filled auto injector pen and, for eligible patients with hemophilia B, the first once weekly subcutaneous prophylactic option.
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