Pfizer Confirms Death Of Patient Enrolled In Hemophilia Drug Study

• Hympavzi was approved by the U.S. Food and Drug Administration (FDA) in October 2024 for routine prophylaxis in adults and adolescents aged 12 years and older with severe hemophilia A or B without inhibitors.
• The patient who died had hemophilia A and inhibitors.
• Pfizer is now actively gathering information to understand the circumstances surrounding the death and identify the cause.

One of the patients enrolled in Pfizer’s trial of Hympavzi in people living with a bleeding disorder died earlier this month, the company said.

The company said in a letter to the World Federation of Hemophilia (WFH) and National Bleeding Disorders Foundation (NBDF) that the patient suffered a fatal thrombotic stroke after a minor surgery on December 14.

Hympavzi was approved by the U.S. Food and Drug Administration (FDA) in October 2024 for routine prophylaxis in adults and adolescents aged 12 years and older with severe hemophilia A or B without inhibitors. Pfizer is now studying Hympavzi in people living with hemophilia A or B irrespective of whether they have inhibitors.

Hemophilia A and B are bleeding disorders, but some patients develop "inhibitors" that stop standard blood clotting factors replacement therapy from working, making bleeds harder to stop. The patient who died had hemophilia A and inhibitors.

The patient participated in the active treatment phase of the parent study in 2022 prior to entering the long-term extension study in 2023, according to Pfizer.

Pfizer’s Next Moves

Pfizer is now actively gathering information to understand the circumstances surrounding the death and identify the cause with the support of the trial investigator and an independent external Data Monitoring Committee. The drugmaker said that regulatory authorities and investigators have been informed.

The World Federation of Hemophilia (WFH) and National Bleeding Disorders Foundation (NBDF)  noted that thrombosis is an adverse event of special interest with Hympavzi due to the drug’s mechanism of action as a rebalancing agent that targets tissue factor pathway inhibitor (TFPI) to increase thrombin generation for clot formation.

“The use of marstacimab (Hympavzi) should include close monitoring for symptoms of thrombosis and other adverse events, especially in surgical settings in combination with clotting factor concentrates or bypassing agents,” they said in a statement.

How Did Stocktwits Users React?

On Stocktwits, retail sentiment around PFE fell from ‘bullish’ to ‘bearish’ territory over the past 24 hours while message volume fell from ‘extremely high’ to ‘normal’ levels.

A Stocktwits user expressed disappointment over the stock trading in the red while major pharma stocks rallied.

PFE stock has dropped nearly 6% this year and by over 6% over the past 12 months. 

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