FDA Approves Pfizer's Hympavzi as First Once-Weekly Subcutaneous Treatment for Hemophilia A and B

The U.S. Food and Drug Administration (FDA) has approved Pfizer Inc.'s Hympavzi (marstacimab-hncq) for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and adolescents aged 12 years and older with hemophilia A (congenital factor VIII deficiency) without factor VIII inhibitors, or hemophilia B (congenital factor IX deficiency) without factor IX inhibitors. The regulatory clearance marks the first approval in the United States of an anti-tissue factor pathway inhibitor (anti-TFPI) for hemophilia and introduces the first prophylactic therapy administered via a pre-filled, once-weekly subcutaneous auto-injector pen.

Hemophilia A and B are rare lifelong genetic bleeding disorders affecting more than 800,000 people globally—including approximately 33,000 individuals in the United States—caused by a deficiency in coagulation factor VIII or factor IX that prevents blood from clotting properly. For decades, standard prophylactic care has required frequent, time-consuming intravenous infusions of replacement clotting factors multiple times per week, imposing a heavy treatment burden on patients and caregivers.

Phase 3 BASIS Trial Demonstrates Significant Bleed Reduction

Rather than replacing the missing clotting protein directly, Hympavzi is a human monoclonal immunoglobulin G1 (IgG1) antibody directed against the Kunitz domain 2 of tissue factor pathway inhibitor (TFPI), a natural anticoagulation protein that blocks the initiation of blood clot formation. By inhibiting TFPI, the therapy enhances thrombin generation through the extrinsic coagulation pathway regardless of whether a patient lacks factor VIII or factor IX, allowing a single flat-dose regimen—a 300 mg loading dose followed by 150 mg once weekly—without weight-based mixing or laboratory monitoring.

The FDA's decision was supported by data from the pivotal Phase 3 BASIS study, which evaluated 116 adult and adolescent patients over a 12-month active treatment period following a six-month observational phase on standard factor replacement. In patients previously treated on-demand with factor replacement, Hympavzi reduced the annualized bleeding rate (ABR) for treated bleeds by 92 percent, from a mean of 38.00 bleeds per year down to 3.18. Among patients switching from routine prophylactic factor infusions, Hympavzi demonstrated non-inferiority and superiority, lowering the mean ABR by 35 percent from 7.85 to 5.08.

“The approval of Hympavzi is a meaningful advancement for people living with hemophilia A or B, delivering effective bleed protection through a simple once-weekly subcutaneous auto-injector pen.” — Aamir Malik, Chief U.S. Commercial Officer and Executive Vice President at Pfizer

Expanding Pfizer's Hematology Portfolio Alongside Gene Therapy

Clinical investigators noted that while Roche's blockbuster bispecific antibody Hemlibra (emicizumab) transformed subcutaneous prophylaxis for hemophilia A, patients with hemophilia B previously lacked a comparable non-factor subcutaneous option in the United States. The FDA's Center for Drug Evaluation and Research highlighted that Hympavzi's pre-filled pen or syringe design minimizes preparation steps and allows patients to self-administer injections at home in seconds.

Hympavzi represents the second major regulatory milestone in Pfizer's hemophilia franchise this year, following the April FDA approval of Beqvez (fidanacogene elaparvovec-dzkt), a one-time gene therapy for adults with moderate-to-severe hemophilia B. Pfizer stated that marketing applications for marstacimab are also under review by the European Medicines Agency (EMA), where the Committee for Medicinal Products for Human Use (CHMP) recently issued a positive opinion, while additional Phase 3 trials are evaluating the medicine in pediatric patients under age 12 and individuals with inhibitors.

Sources

• U.S. Food and Drug Administration
• Pfizer Inc.