A patient in a clinical trial for Pfizer’s recently approved hemophilia treatment, Hympavzi (marstacimab), has died following a stroke adn brain hemorrhage, raising new scrutiny of the drug’s safety profile. The death, reported by the European Hemophilia Consortium, occurred December 14 and involves a participant enrolled in a study evaluating Hympavzi’s effectiveness in individuals with hemophilia A or B [[1]]. pfizer, which received FDA approval for Hympavzi in 2023, is investigating the circumstances surrounding the death while maintaining that current data does not suggest a widespread safety concern [[2]], though a separate reported death occurred in december 2025 [[3]].
A patient participating in a clinical trial for Pfizer’s hemophilia treatment, Hemfabvze, died on December 14 following a stroke and subsequent brain hemorrhage, according to the European Hemophilia Consortium, a patient support group.
The patient was enrolled in a study evaluating Hemfabvze in individuals with hemophilia A or B, with or without inhibitors. The drug is administered via weekly injection and targets blood clotting proteins.
Pfizer stated, “We are working with the investigational study sponsor and the independent Data Monitoring Committee to actively gather information to better understand the complex and multi-factorial circumstances surrounding this event.” The company’s response underscores the rigorous safety protocols in place for clinical trials, particularly for novel therapies.
Hemfabvze received approval from the United States Food and Drug Administration last year for the prevention or reduction of bleeding episodes in patients age 12 and older with hemophilia A or B. The treatment represents a significant advancement in managing this rare genetic disorder, offering a potential alternative to traditional therapies.
Based on current knowledge and the overall clinical data collected to date, Pfizer does not anticipate any impact on the safety of patients who have been treated with the drug. The company continues to monitor the situation closely and will provide updates as more information becomes available.
