FDA Approval

Marstacimab-hncq (Hympavzi) Gains FDA Approval for Expanded Hemophilia A and B Indication in Patients Aged 6 Years and Older

Anthony Calabro, MA

Key Highlights

  • Marstacimab-hncq (hympavzi) is now approved for routine prophylaxis in adults and pediatric patients aged 6 years and older with hemophilia A or B, with or without inhibitors.
  • The approval was supported by the phase 3 BASIS and BASIS KIDS trials.
  • In BASIS, marstacimab-hncq reduced the mean treated annualized bleeding rate by 93% vs on-demand intravenous bypassing agents in patients aged 12 years and older with inhibitors.
  • Common adverse reactions included injection site reaction, headache, pyrexia, arthralgia, diarrhea, pruritus, and rash.

On June 8, 2026, the FDA approved an expanded indication for marstacimab-hncq (Hympavzi; Pfizer Inc) for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and pediatric patients aged 6 years and older with hemophilia A, with or without factor VIII inhibitors, or hemophilia B, with or without factor IX inhibitors. The expanded indication includes patients aged 12 years and older with inhibitors and pediatric patients aged 6 to 11 years, with or without inhibitors.

Marstacimab-hncq is administered subcutaneously once weekly and does not require routine treatment-related laboratory monitoring, according to the announcement. The application received FDA Priority Review. The FDA also granted breakthrough therapy designation for routine prophylaxis in pediatric patients aged at least 6 years and younger than 12 years with hemophilia B, with or without inhibitors.

The approval in adults and adolescents aged 12 years and older with hemophilia A or B with inhibitors was supported by results from the global phase 3, open-label, multicenter BASIS trial. In the inhibitor cohort, 48 patients received marstacimab-hncq during a 12-month active treatment period, compared with an on-demand intravenous regimen with bypassing agents, administered as usual care, during a 6-month observational period. The primary endpoint was the treated annualized bleeding rate. Marstacimab-hncq reduced the mean treated annualized bleeding rate by 93% compared with on-demand intravenous bypassing agents: 1.4 (95% CI, 0.9-2.3) vs 19.8 (95% CI, 16.1-24.3; P < .0001).

Interim results from the phase 3, open-label BASIS KIDS trial supported approval in children aged 6 to 17 years with hemophilia A or B, with or without inhibitors. Among children without inhibitors, the mean treated annualized bleeding rate was 1.8 (99% CI, 1.1-2.6) with marstacimab-hncq compared with a historical model-based mean treated annualized bleeding rate of 3.6 (99% CI, 1.3-5.8) with routine prophylaxis. Among children with inhibitors, the mean treated annualized bleeding rate was 1.4 (99% CI, 0.5-4.5) with marstacimab-hncq compared with 18.9 (99% CI, 14.2-25.2) with on-demand therapy.

The most commonly reported adverse reactions, occurring in at least 2% of adult and pediatric patients aged 6 years and older, with or without inhibitors, were injection-site reactions, headache, pyrexia, arthralgia, diarrhea, pruritus, and rash. Thromboembolic events, including venous and arterial events, occurred in 2 of 259 patients who received marstacimab-hncq in the open-label extension study.

The US label includes warnings and precautions for thromboembolic events, hypersensitivity, embryofetal toxicity, and increased fibrin D-dimer and prothrombin fragment 1.2 laboratory values.

In BASIS, patients received a 300-mg subcutaneous loading dose followed by 150 mg subcutaneously once weekly. In BASIS KIDS, patients aged 6 to 11 years received a 150-mg subcutaneous loading dose followed by 75 mg subcutaneously once weekly; patients aged 12 to 17 years received a 300-mg loading dose followed by 150 mg subcutaneously once weekly.

Reference
Pfizer. U.S. FDA approves Pfizer’s HYMPAVZI for the treatment of two additional hemophilia A or B patient populations with significant medical need. Published June 8, 2026. Accessed June 8, 2026. https://www.pfizer.com/news/press-release/press-release-detail/us-fda-approves-pfizers-hympavzi-treatment-two-additional