FDA approves Pfizer’s HYMPAVZI for two additional hemophilia A and B patient populations with significant unmet need

The U.S. FDA has recently granted an expanded indication for HYMPAVZI (marstacimab-hncq), extending its use to patients with hemophilia A or B aged 12 and older who have inhibitors, and to pediatric patients between the ages of 6 and 11 with or without inhibitors. HYMPAVZI is now indicated across the U.S. for routine prophylaxis aimed at preventing or reducing the frequency of bleeding episodes in adults and pediatric patients aged 6 and above with hemophilia A or hemophilia B, regardless of inhibitor status. The therapy provides bleed protection through once-weekly subcutaneous administration, eliminating the need for routine treatment-related laboratory monitoring.

“For children who have to deal with bleeding episodes from an early age and for people living with hemophilia who develop inhibitors, treatment options have been limited and are often burdensome,” said Guy Young, M.D., Director, Hemostasis and Thrombosis Center at Children’s Hospital, Los Angeles. “A treatment that can reduce bleeding with straightforward, once-weekly administration has the potential to fundamentally change how patients and caregivers approach this disease, offering control with a level of simplicity this community has long needed.”

Hemophilia is a condition most commonly identified in early childhood and affects more than 800,000 people globally. When the blood is unable to clot as it should, patients face an elevated risk of painful bleeding episodes, including within the joints, which over time can lead to scarring and lasting damage. In children particularly, whose joints contain actively developing cartilage and bone, the consequences of repeated bleeds can be especially harmful.

Among those living with hemophilia, the development of inhibitors to factor replacement therapy narrows the already limited pool of treatment options and raises the risk of uncontrolled bleeding. These inhibitory antibodies arise in roughly 20% of people with hemophilia A and around 3% of those with hemophilia B. For many affected individuals, factor replacement therapies eventually lose their ability to prevent or halt bleeding episodes, a challenge that is particularly acute for those who do not respond to immune tolerance induction therapy.

“With this expanded approval, we believe HYMPAVZI can become a transformative option and meet a significant medical need for people living with hemophilia A or B with or without inhibitors ages 6 years and older. Particularly for children ages 6 to 11 with hemophilia B who will now, for the first time, have a subcutaneous non-factor treatment available,” said Aamir Malik, Chief U.S. Commercial Officer and Executive Vice President, Pfizer. “This milestone represents the latest step in Pfizer’s more than 40-year commitment to advancing care and quality of life for people living with hemophilia, which began with the introduction of recombinant therapies and has evolved with the introduction of this once-weekly subcutaneous treatment.”

Data from the Phase 3 BASIS trial underpinned the approval of HYMPAVZI in adults and adolescents aged 12 and older with hemophilia A or B carrying inhibitors. The trial showed HYMPAVZI to be superior in improving key bleeding outcomes, with the mean treated annualized bleeding rate (ABR) slashed by 93% relative to on-demand intravenous treatment with bypassing agents (1.4 vs. 19.8; p<0.0001).

Interim findings from the Phase 3 BASIS KIDS trial provided the foundation for approval in children aged 6 to 17 with hemophilia A or B with or without inhibitors. Descriptive analyses of patients who received HYMPAVZI indicated the following:

• Among children aged 6 to 17 without inhibitors, a mean treated ABR of 1.8 was recorded with HYMPAVZI, against a historical model-based mean of 3.6 among those on routine prophylaxis
• Among children aged 6 to 17 with inhibitors, a mean treated ABR of 1.4 was observed with HYMPAVZI, against a historical model-based mean of 18.9 among those on on-demand therapy
• Among children aged 6 to 11 with inhibitors previously on on-demand therapy, or without inhibitors previously on routine prophylaxis, model-based mean treated ABRs of 1.3 and 1.4 were recorded respectively, with a median ABR of 1.0 in both groups

The most commonly reported adverse reactions in adult and pediatric patients aged 6 and older, with or without inhibitors, were injection site reaction, headache, pyrexia, arthralgia, diarrhoea, pruritus, and rash. Two thromboembolic events were observed among 259 patients who received HYMPAVZI in an open-label extension study. Thromboembolic events, hypersensitivity, embryofetal toxicity, and raised laboratory values of fibrin D-dimer and prothrombin fragment 1.2 are captured within the Warnings and Precautions section of the U.S. label.

The HYMPAVZI application was reviewed under FDA Priority Review, a designation reserved for medicines addressing serious conditions where meaningful improvements in safety or effectiveness over existing options can be demonstrated. The FDA additionally granted HYMPAVZI Breakthrough Therapy Designation for routine prophylaxis in younger pediatric patients aged 6 to under 12 with hemophilia B, with and without inhibitors, a pathway designed to accelerate development and review of therapies showing early promise on clinically significant endpoints.

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