A patient enrolled in Pfizer’s long‑term extension study of the hemophilia drug Hympavzi (marstacimab) died on December 14, 2025, after experiencing a stroke and intracranial bleeding. The death was reported by Pfizer’s clinical development team on December 23, 2025, and the company is investigating the circumstances.
The deceased patient had hemophilia A with inhibitors and had previously participated in the Phase III BASIS trial in 2022 before moving to the extension phase in 2023. The patient’s medical history included co‑existing conditions and concurrent medications, factors that Pfizer noted may have contributed to the adverse event.
Pfizer has engaged its data monitoring committee and is conducting a thorough investigation. The company stated that it is reviewing the patient’s full medical record, the timing of the adverse event relative to drug dosing, and any potential interactions with other therapies. No definitive causal link to Hympavzi has been established yet.
Regulatory authorities, including the U.S. Food and Drug Administration and the European Medicines Agency, have not yet issued formal requests for additional data, but the incident could prompt enhanced scrutiny and additional safety reporting requirements. Pfizer has indicated it will cooperate fully with any regulatory inquiries.
The death raises significant safety concerns for Hympavzi, a drug recently approved for hemophilia A and B patients without inhibitors. A fatal event in a long‑term study may delay future regulatory approvals, affect the drug’s commercial prospects, and erode investor confidence in Pfizer’s hemophilia pipeline. Competitors in the hemophilia market may view this as an opportunity to strengthen their market position.
Investors reacted negatively to the announcement, with analysts expressing caution over the potential impact on Hympavzi’s development trajectory and the broader implications for Pfizer’s hemophilia strategy.
The content on BeyondSPX is for informational purposes only and should not be construed as financial or investment advice. We are not financial advisors. Consult with a qualified professional before making any investment decisions. Any actions you take based on information from this site are solely at your own risk.