Global pharma powerhouse Pfizer has said the US FDA has accepted and granted Priority Review for its application seeking to broaden the use of HYMPAVZI (marstacimab) to younger and harder-to-treat hemophilia patients, a move that could significantly expand treatment options if approved.
The supplemental Biologics License Application aims to extend HYMPAVZI’s indication to include patients ages 6 and older with hemophilia A or B who have developed inhibitors, as well as children ages 6 to 11 with hemophilia A or B without inhibitors.
HYMPAVZI is already approved in the US for patients 12 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 decision date in the second quarter of 2026. If approved, the therapy would provide bleed protection through a once-weekly subcutaneous injection, with minimal preparation and no routine treatment-related laboratory monitoring—an advantage for patients with limited or burdensome treatment options.
“There is a significant medical need for younger patients with hemophilia and for those who have developed inhibitors, which neutralize factor replacement therapies and render them ineffective,” said Michael Vincent, Chief Inflammation & Immunology Officer, Pfizer.
"Based on the findings in the BASIS clinical trial program and if approved, we believe HYMPAVZI has the potential to become a transformative option for these patients that have limited or burdensome treatment options today. We look forward to progressing discussions with regulators to make this medicine available for patients.”
Hemophilia, typically diagnosed in early childhood, affects more than 800,000 people worldwide. The disorder prevents normal blood clotting, increasing the risk of painful bleeding episodes, including joint bleeds that can lead to long-term damage. Children are especially vulnerable because repeated bleeding can interfere with growing cartilage and bone.
“For children living with hemophilia A or B between ages 6 and 11, treatment approaches that prevent bleeds are particularly important to protect growing joints,” said Guy Young, Director, Hemostasis and Thrombosis Center at Children's Hospital, Los Angeles.
“HYMPAVZI would address a critical unmet medical need for these patients and those with inhibitors if approved, particularly patients ages 6 to 11 with hemophilia B who do not have non-factor treatment options available today.”
The Priority Review designation shortens the FDA’s standard review timeline by four months and is reserved for therapies that may offer major advances or address unmet medical needs.
HYMPAVZI has also received Breakthrough Therapy Designation for routine prophylaxis in pediatric patients ages 6 to under 12 with hemophilia B, with or without inhibitors, reflecting preliminary evidence that the therapy could substantially improve outcomes compared with existing treatments.
Pfizer’s submission is supported by Phase 3 data from the BASIS trial program, including the inhibitor cohort of the BASIS study in adolescents and adults and the BASIS KIDS trial in children ages 6 to 11. Separately, HYMPAVZI is also under review by the European Medicines Agency for use in patients 12 and older with hemophilia A or B who have inhibitors.
