Pfizer Notifies Hemophilia Community of Patient Death in Study of Hympavzi

Rare Daily Staff

A patient receiving Pfizer’s hemophilia drug Hympavzi as part of a long‑term extension trial has died, according to a letter the company sent to the hemophilia patient community.

The patient, who had hemophilia and was enrolled in a long‑term extension trial of Hympavzi, died on Dec. 14 after serious adverse events, including a stroke followed by a brain hemorrhage.

Hemophilia is a rare, genetic, life-threatening bleeding disorder caused by a lack of adequate clotting factors — proteins that help stop bleeding. People with the condition are particularly vulnerable to bleeding in their joints, muscles, and internal organs, leading to pain, swelling, and joint damage. Treatments aim to temporarily replace or supplement low levels of the clotting factor.

Hympavzi, discovered by Pfizer scientists, has a mechanism of action that differs from factor VIII and factor IX replacement therapies. Instead of replacing missing or insufficient clotting factors, Hympavzi targets tissue factor pathway inhibitor (TFPI), a natural protein that limits the initiation of blood clotting. By inhibiting the Kunitz 2 domain of TFPI, the therapy may help restore balance between bleeding and clot formation, aiming to provide strong bleed protection, good tolerability, and straightforward administration.

The U.S. Food and Drug Administration approved Hympavzi in October 2024 for routine prophylaxis to prevent or reduce bleeding episodes in adults and adolescents with hemophilia A without factor VIII inhibitors, or hemophilia B without factor IX inhibitors.