Quick Summary
1. Announcement: The FDA has granted Priority Review to Pfizer’s supplemental Biologics License Application (sBLA) for HYMPAVZI™ (marstacimab).
2. Target Groups: The expansion covers patients 6+ years with inhibitors (Hemophilia A/B) and children ages 6–11 without inhibitors.
3. Key Milestone: If approved, HYMPAVZI will be the first non-factor prophylactic treatment for children (6–11) with Hemophilia B.
4. Administration: A once-weekly, subcutaneous injection using a pre-filled pen, requiring no routine lab monitoring.
5. Timeline: The FDA’s decision (PDUFA date) is expected in the second quarter of 2026.
6. Clinical Basis: Supported by Phase 3 data from the BASIS and BASIS KIDS trials showing significant bleed protection.
Pfizer Inc. announced today that the U.S. Food and Drug Administration (FDA) has accepted and granted Priority Review for a supplemental Biologics License Application (sBLA) for HYMPAVZI™ (marstacimab). The application seeks to expand the drug’s current indication to include hemophilia A or B patients 6 years and older with inhibitors, as well as pediatric patients aged 6 to 11 without inhibitors.
Currently, HYMPAVZI is approved in the U.S. for patients 12 and older with hemophilia A or B without inhibitors. This new regulatory milestone moves Pfizer closer to providing a much-needed alternative for younger children and those whose bodies have developed resistance to standard factor replacement therapies.
Addressing an Urgent Unmet Need
Hemophilia is a rare genetic blood disorder that prevents normal clotting, often leading to painful joint bleeds and long-term damage. While factor replacement has been the standard of care for decades, approximately 20% of hemophilia A patients and 3% of hemophilia B patients develop “inhibitors” antibodies that neutralize the replacement factors and render them ineffective.
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A New Standard for Pediatric Care
For the hemophilia B community, the approval would be historic. HYMPAVZI would become the first non-factor prophylactic treatment available for children aged 6 to 11 with hemophilia B. This is particularly critical as children’s growing joints are highly susceptible to damage from repeated bleeding episodes.
The FDA has also granted HYMPAVZI Breakthrough Therapy Designation for the prevention of bleeding episodes in pediatric patients (ages 6 to <12) with hemophilia B, regardless of inhibitor status.
Clinical Trial Foundations
The submission is backed by robust data from two pivotal Phase 3 studies:
- BASIS Trial: Focused on efficacy and safety in adults and adolescents (12+) with inhibitors.
- BASIS KIDS Trial: Evaluated children (6–11) both with and without inhibitors.
In these trials, marstacimab demonstrated a significant reduction in the annualized bleeding rate (ABR) compared to traditional on-demand bypassing agents or routine factor prophylaxis.
Read More: Pfizer’s HYMPAVZI™ Shows Strong Efficacy in Late-Stage Hemophilia Trial
Mechanism of Action
Unlike traditional therapies that replace missing clotting factors (Factor VIII or IX), HYMPAVZI is a monoclonal antibody that targets tissue factor pathway inhibitor (TFPI). By blocking TFPI, the drug helps the body re-establish a natural balance between bleeding and clotting, providing continuous protection through a simple, once-weekly subcutaneous injection.
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What’s Next?
The FDA’s Priority Review status shortens the review period by four months, with a final decision expected in Q2 2026. Simultaneously, the European Medicines Agency (EMA) is reviewing the drug for use in adults and adolescents with inhibitors.
If approved, the expanded label will offer a more convenient, less burdensome treatment path for families, eliminating the need for frequent intravenous infusions and routine laboratory monitoring.
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