Pfizer’s HYMPAVZI (marstacimab) gains FDA Priority Review for expanded use in pediatric hemophilia A/B (ages 6+) with/without inhibitors. BASIS trial data shows bleed reductions. PDUFA Q2 2026.
Written By: Samiksha Jadhav BPharm
Reviewed By: Pharmacally Editorial Team
Pfizer Inc. announced that the U.S. Food and Drug Administration has accepted and granted Priority Review to a supplemental Biologics License Application (sBLA) for HYMPAVZI® (marstacimab).
The sBLA seeks to expand HYMPAVZI’s indication to patients aged 6 years and older with hemophilia A or B with inhibitors, and children aged 6 to 11 years with hemophilia A or B without inhibitors. HYMPAVZI is currently approved in the U.S. for patients 12 years and older with hemophilia A or B without FVIII or FIX inhibitors. The FDA set a PDUFA action date in Q2 2026.
Pfizer’s Chief Inflammation and Immunology Officer, Michael Vincent, noted the unmet need in younger hemophilia patients and those with inhibitors unresponsive to factor therapy. He cited BASIS trial results suggesting HYMPAVZI could provide a meaningful new option for patients with limited choices, pending approval.
Clinical Basis for Priority Review
The application draws from Pfizer’s Phase 3 BASIS trial program.
Adults and adolescents with inhibitors: BASIS inhibitor cohort data (NCT03938792) showed HYMPAVZI reduced annualized bleeding rates (ABR) versus prior on-demand bypassing therapy.
Pediatric patients aged 6 to 11 years: BASIS KIDS trial demonstrated effective bleed prevention compared to prior prophylaxis or on-demand regimens.
BASIS KIDS Trial Overview
This global, Phase 3 (NCT05611801), open-label study evaluated HYMPAVZI’s safety and efficacy in children aged 1 to under 18 years with severe hemophilia A or moderately severe to severe hemophilia B, with or without inhibitors. The submission highlights 68 children aged 6 to 11 years on 12 months of HYMPAVZI prophylaxis versus prior care (factor therapy or bypassing agents).
Patients received a subcutaneous loading dose followed by weekly maintenance, with optional dose escalation. The primary endpoint treated ABR supported HYMPAVZI as a simplified prophylactic option.
Guy Young, Director of the Hemostasis and Thrombosis Center at Children’s Hospital Los Angeles, stressed bleed prevention’s role in protecting children’s developing joints. If approved, he said, HYMPAVZI could address a major gap, especially for pediatric hemophilia B patients lacking non-factor prophylaxis.
Additional Regulatory Momentum
The FDA also granted Breakthrough Therapy Designation to HYMPAVZI for routine prophylaxis in children aged 6 to under 12 years with hemophilia B, with or without inhibitors, to expedite review.
HYMPAVZI is under European Medicines Agency review for patients 12+ with hemophilia A or B with inhibitors.
Mechanism and Clinical Context
HYMPAVZI inhibits TFPI’s Kunitz-2 domain to rebalance hemostasis, bypassing the need for factor replacement ideal for inhibitor patients.
References
FDA Grants Priority Review for HYMPAVZI® (marstacimab) sBLA for the Treatment of Two Hemophilia A or B Patient Populations with Significant Medical Need, 06 February 2026, FDA Grants Priority Review for HYMPAVZI® (marstacimab) sBLA for the Treatment of Two Hemophilia A or B Patient Populations with Significant Medical Need | Pfizer
A Clinical Trial of Study Medicine (Marstacimab) in Pediatric Patients With Hemophilia A or Hemophilia B (BASIS KIDS), ClinicalTrials.gov ID NCT05611801, https://clinicaltrials.gov/study/NCT05611801
Pfizer’s HYMPAVZI Shows 93% Bleed Reduction in Hemophilia A/B with Inhibitors: Key Data from the BASIS Trial, 07 December 2025, https://pharmacally.com/pfizers-hympavzi-shows-93-bleed-reduction-in-hemophilia-a-b-with-inhibitors-key-data-from-the-basis-trial/
Study of the Efficacy and Safety PF-06741086 in Adult and Teenage Participants With Severe Hemophilia A or Moderately Severe to Severe Hemophilia B, ClinicalTrials.gov ID NCT03938792, Study Details | NCT03938792 | Study of the Efficacy and Safety PF-06741086 in Adult and Teenage Participants With Severe Hemophilia A or Moderately Severe to Severe Hemophilia B | ClinicalTrials.gov