Pfizer has secured an expanded approval from the U.S. Food and Drug Administration (FDA) for HYMPAVZI® (marstacimab-hncq), broadening access to the once-weekly treatment for additional patients living with hemophilia A and hemophilia B.
The new approval extends HYMPAVZI’s indication to include patients aged 12 years and older with hemophilia A or B who have inhibitors, as well as pediatric patients aged 6 to 11 years with or without inhibitors. The expanded label means the therapy can now be used as routine prophylaxis to prevent or reduce bleeding episodes in adults and children aged six years and older with hemophilia A or B, regardless of inhibitor status.
The decision marks a significant milestone in hemophilia care, particularly for younger patients and those who develop inhibitors to traditional factor replacement therapies. Inhibitors are antibodies that neutralize the effectiveness of clotting factor treatments, leaving patients with limited therapeutic options and an increased risk of uncontrolled bleeding.
HYMPAVZI offers a once-weekly subcutaneous injection designed to provide bleed protection without the need for routine treatment-related laboratory monitoring. The convenience of self-administered weekly dosing could help reduce the burden of treatment for patients and caregivers compared with more frequent intravenous therapies.
Hemophilia is a rare inherited bleeding disorder that affects more than 800,000 people worldwide. The condition is typically diagnosed during childhood and results from deficiencies in clotting factors VIII or IX, impairing the body’s ability to form blood clots. Recurrent bleeding episodes, particularly into joints, can lead to chronic pain, joint damage, and long-term disability.
Experts say the approval addresses an important unmet need within the hemophilia community. Guy Young, M.D., Director of the Hemostasis and Thrombosis Center at Children’s Hospital Los Angeles, noted that treatment options for children and patients with inhibitors have historically been limited and often burdensome. He emphasized that a therapy capable of reducing bleeding with simple weekly administration has the potential to change how patients manage the disease.
The FDA’s decision was supported by data from the Phase 3 BASIS clinical program. Results from the BASIS trial involving adolescents and adults with hemophilia A or B and inhibitors demonstrated that HYMPAVZI significantly reduced bleeding rates. Patients receiving the therapy achieved a 93% reduction in mean treated annualized bleeding rate (ABR) compared with on-demand intravenous treatment using bypassing agents.
Additional support came from interim findings from the Phase 3 BASIS KIDS trial, which evaluated HYMPAVZI in children aged 6 to 17 years. Among pediatric patients without inhibitors, treatment resulted in a mean treated annualized bleeding rate of 1.8, compared with a historical rate of 3.6 observed with routine prophylaxis. For children with inhibitors, the mean treated annualized bleeding rate was 1.4, substantially lower than the historical rate of 18.9 associated with on-demand therapy.
Notably, children aged 6 to 11 years demonstrated particularly low bleeding rates, with model-based mean treated annualized bleeding rates ranging from 1.3 to 1.4 and median rates of 1.0.
The safety profile of HYMPAVZI was generally consistent across adult and pediatric populations. The most commonly reported adverse reactions included injection-site reactions, headache, fever, joint pain, diarrhea, itching, and rash. Pfizer noted that thromboembolic events were observed in two patients among 259 participants treated during an open-label extension study.
The application received FDA Priority Review, a designation reserved for therapies that may offer significant improvements over existing treatment options for serious conditions. HYMPAVZI also previously received Breakthrough Therapy Designation for younger pediatric patients with hemophilia B, reflecting its potential to address a critical unmet need.
Aamir Malik, Pfizer’s Chief U.S. Commercial Officer, said the expanded approval reinforces the company’s more than four-decade commitment to advancing hemophilia care. He highlighted that children aged 6 to 11 years with hemophilia B now have access, for the first time, to a non-factor subcutaneous treatment option that can be administered weekly.
With this latest regulatory milestone, Pfizer aims to further transform hemophilia management by providing a simpler and more convenient prophylactic treatment option for a broader range of patients living with the lifelong bleeding disorder.