Pfizer’s HYMPAVZI Shows 93% Reduction In Bleeding For Hemophilia Patients With Inhibitors In Phase 3 Study

Pfizer has released new Phase 3 data from its BASIS study evaluating HYMPAVZI® (marstacimab) in adults and adolescents with hemophilia A or B who have developed inhibitors to factor replacement therapies. The trial demonstrated that HYMPAVZI delivered once-weekly via subcutaneous injection resulted in significantly better bleeding control compared to on-demand treatment with bypassing agents, marking a major advance for a group of patients with limited therapeutic options.

Inhibitors remain one of the most challenging complications of hemophilia care, rendering standard factor replacement ineffective for about 20% of patients with hemophilia A and 3% with hemophilia B. In the BASIS trial, 48 participants first underwent a six-month observational phase on standard intravenous bypassing agents before switching to HYMPAVZI for the 12-month active treatment period. HYMPAVZI was given as a 300 mg loading dose followed by weekly 150 mg injections.

“The emergence of inhibitors poses significant treatment challenges and can increase disease burden for people living with hemophilia A or B,”4 said Davide Matino, M.D., M.Sc., BASIS Principal Investigator, Associate Professor of Medicine, McMaster University. “In patients with inhibitors, this study demonstrates HYMPAVZI’s potential as a safe and efficacious treatment option that not only significantly reduced bleeding episodes via a once-weekly subcutaneous administration, but also demonstrated improvement in certain aspects of health-related quality of life.”

Results showed a 93% reduction in mean treated annualized bleeding rate (ABR) with HYMPAVZI compared to prior on-demand therapy, with a median ABR of 0 during the treatment phase. Superiority was consistently observed across all key bleeding endpoints, including spontaneous bleeds, joint bleeds, and total bleeds, and across hemophilia type, age groups, and global regions. HYMPAVZI also delivered meaningful quality-of-life improvements, with clinically significant gains across Haem-A-QoL domains and the EQ-5D-5L assessments.

HYMPAVZI was generally well tolerated, with no deaths or thromboembolic events in the safety population. Most adverse events were mild or moderate, with COVID-19, upper respiratory tract infections, elevated D-dimer, and headache being the most common. Data from the study have been submitted to both the FDA and EMA. HYMPAVZI is already approved in more than 40 countries for patients 12 years and older with hemophilia A or B without inhibitors, and these new findings support potential expansion into the inhibitor population.

“It is encouraging that these data demonstrate the potential of HYMPAVZI to combine efficacy, safety, and straightforward administration for adults and adolescents living with hemophilia A or B with inhibitors and address a significant patient need,” said Michael Vincent, M.D., Ph.D., Chief Inflammation & Immunology Officer, Pfizer. “We look forward to potentially making this treatment available for these patients as Pfizer continues its ongoing effort spanning more than 40 years to improve hemophilia care.”