The US FDA has expanded approval of Pfizer’s HYMPAVZI (marstacimab-hncq), widening its use to patients aged 12 and above with hemophilia A or B who have inhibitors, and pediatric patients aged 6 to 11 with or without inhibitors.

 

The decision marks a major shift in treatment access, making HYMPAVZI the first subcutaneous non-factor therapy available for pediatric hemophilia B patients aged 6 to 11.

 

Pfizer announced the expanded indication on Monday, saying the therapy is now approved in the US for routine prophylaxis to prevent or reduce bleeding episodes in adults and children aged 6 and older living with hemophilia A or B, with or without inhibitors.

 

HYMPAVZI is administered once weekly via subcutaneous injection and does not require routine treatment-related lab monitoring, offering a simpler alternative to traditional factor replacement therapies.

 

“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, 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 affects more than 800,000 people worldwide and is typically diagnosed in early childhood. The disorder prevents proper blood clotting, leading to painful and sometimes damaging bleeding episodes, particularly in joints that are still developing.

 

Complications are more severe for patients who develop inhibitors—antibodies that neutralize standard clotting factor treatments. These occur in roughly 20% of hemophilia A patients and about 3% of those with hemophilia B, often leaving patients with fewer effective treatment options.

 

“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 US 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.”

 

The approval is backed by Phase 3 data from the BASIS and BASIS KIDS clinical trials, which showed substantial reductions in annualized bleeding rates compared to standard on-demand or prior prophylactic therapies.

 

In adult and adolescent patients with inhibitors, HYMPAVZI reduced mean treated bleeding rates by 93% compared to bypassing agents.

 

In pediatric studies, treated annualized bleeding rates dropped to around 1–2 episodes per year across both inhibitor and non-inhibitor groups, including in children as young as six.

 

Safety findings were consistent with previous studies, with injection site reactions, headache, fever, joint pain, and rash among the most commonly reported side effects. Rare thromboembolic events were observed in clinical studies and are included in the prescribing warnings.

 

HYMPAVZI works differently from traditional therapies. Instead of replacing missing clotting factors, it targets tissue factor pathway inhibitor (TFPI), helping restore balance in the body’s clotting system.

 

With this expansion, HYMPAVZI becomes one of the few advanced non-factor therapies available for both adult and pediatric hemophilia populations, further intensifying competition in a rapidly evolving treatment landscape.