HYMPAVZI Significantly Reduces Bleeding in Hemophilia A and B Patients with Inhibitors, Phase 3 Trial Shows

Pfizer has announced highly promising results from its Phase 3 BASIS clinical trial (NCT03938792), highlighting the efficacy of HYMPAVZI™ (marstacimab) in significantly reducing bleeding episodes in patients with hemophilia A or B complicated by inhibitors. These inhibitors are antibodies that interfere with traditional clotting factor replacement therapies, making treatment especially challenging.

The study focused on once-weekly subcutaneous injections of HYMPAVZI in adolescents and adults aged 12 years and older. In a head-to-head comparison with standard on-demand therapy—where patients receive bypassing agents only during active bleeding—HYMPAVZI showed dramatic benefits.

Key findings include:

A 93% reduction in annualized bleeding rate (ABR), from 19.78 bleeds per year on on-demand therapy to just 1.39 with HYMPAVZI.
The results were both statistically significant and clinically meaningful (p < 0.0001).
The reduction was consistent across all types of bleeds: spontaneous, joint, target-joint, and total bleeding episodes.

The therapy was generally well tolerated, with a safety profile consistent with earlier Phase 1/2 studies and data from patients without inhibitors. Importantly, no deaths or thromboembolic (clotting) events were reported during the trial.

Dr. Davide Matino, lead investigator from McMaster University, stated:
“Patients who are most in need of a simple and reliable treatment now have a highly promising option. HYMPAVZI’s once-weekly subcutaneous injection has the potential to significantly ease the treatment burden.”

Michael Vincent, Pfizer’s Chief Inflammation & Immunology Officer, also highlighted the broader impact:

“These results address a critical unmet need and demonstrate HYMPAVZI’s potential to help people living with hemophilia A or B with inhibitors.”

With these results, HYMPAVZI is positioned as a major advancement in the treatment of hemophilia with inhibitors—offering a simplified, effective, and well-tolerated option for long-term bleeding control.