Pfizer Secures FDA Priority Review For HYMPAVZI Expansion In Pediatric And Inhibitor Haemophilia Patients

Pfizer announced that the U.S. Food and Drug Administration has accepted and granted Priority Review to its supplemental Biologics License Application for HYMPAVZI (marstacimab). The company is seeking to broaden the drug’s use to include people aged six years and older with hemophilia A or B who have inhibitors, as well as children aged six to eleven without inhibitors. HYMPAVZI is already approved in the U.S. for patients aged 12 and above without inhibitors. The FDA has set a regulatory decision date in the second quarter of 2026.

If cleared, the expanded indication would make HYMPAVZI available to younger and more complex patient groups, offering once-weekly subcutaneous dosing with minimal preparation and no routine lab monitoring. This could be especially meaningful for children and patients with inhibitors, who often face limited treatment options and higher risks of bleeding-related joint damage.

“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, M.D., Ph.D., 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.”

The Priority Review status shortens the FDA’s evaluation timeline, reflecting the therapy’s potential to provide meaningful advances in care. HYMPAVZI has also received Breakthrough Therapy Designation for preventing bleeding in pediatric patients with hemophilia B, both with and without inhibitors, a move designed to speed development and review for serious conditions where early data suggest major benefit.

“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, M.D., 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.”

Pfizer’s submission is supported by Phase 3 data from the BASIS and BASIS KIDS trials, which evaluated the therapy’s safety and effectiveness in adults, adolescents and children. Meanwhile, regulators in Europe are also reviewing HYMPAVZI for use in older patients with inhibitors, underscoring the growing global regulatory momentum behind the medicine.