Pfizer's Hympavzi (marstacimab-hncq) has received approval in the United States for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and children, ages 12 and older, with hemophilia A or B who have not developed inhibitors. This approval marks a significant advancement in hemophilia treatment, offering a novel, convenient administration route compared to traditional factor replacement therapies.
Hympavzi is the first treatment for hemophilia A or B available in a single-dose, prefilled syringe or pen, designed for subcutaneous injection by patients or caregivers. Younos Abdulsattar, Pfizer’s U.S. rare disease medical lead, noted that Hympavzi will offer straightforward, once-weekly subcutaneous administration via an autoinjector pen with minimal preparation required.
Mechanism of Action and Clinical Significance
Unlike factor replacement treatments that supply the missing clotting protein (factor VIII in hemophilia A and factor IX in hemophilia B), Hympavzi reduces the activity of a protein that inhibits blood clot formation. By reducing this protein's activity, Hympavzi promotes blood clotting, thereby preventing or reducing the frequency of bleeding episodes. This non-factor approach represents a significant shift in hemophilia management.
The approval was based on data from the Phase 3 BASIS trial (NCT03938792), which evaluated Hympavzi in males with hemophilia A or B, with or without inhibitors. Patients on on-demand factor replacement therapy who switched to Hympavzi experienced a 92% reduction in the annualized bleeding rate for treated bleeds. Furthermore, Hympavzi outperformed routine prophylaxis with factor replacement, demonstrating a 35% reduction in the annualized rate of treated bleeds.
Long-Term Efficacy and Ongoing Studies
An interim analysis of 107 patients without inhibitors who enrolled in an open-label extension study (NCT05145127) showed a mean annualized bleeding rate of 3.06 over nearly two years. Patients initially on on-demand factor replacement saw their treated bleed rates decrease from 38 to 3.7, while those on routine prophylaxis experienced a reduction from 7.85 to 2.79.
Pfizer is also conducting the BASIS KIDS trial (NCT05611801) to assess the safety and efficacy of Hympavzi in children as young as 12 months with hemophilia A or B, with or without inhibitors. Results from this study are expected in 2028.
Regulatory Status and Availability
Hympavzi is currently under regulatory review in the European Union, where it has received a positive opinion from the European Medicines Agency (EMA) advisory committee, and in other countries. The wholesale acquisition cost of Hympavzi is $795,600 per year, comparable to existing prophylactic treatments for hemophilia A or B. Pfizer will offer a copay assistance program to help eligible patients reduce their out-of-pocket costs.
