NEW YORK — A patient enrolled in a long-term study of Pfizer’s hemophilia drug Hympavzi has died after experiencing serious side effects, the company said.

Pfizer confirmed the patient died on Dec. 14 after suffering a stroke followed by a brain hemorrhage, according to the European Haemophilia Consortium, a patient advocacy group.

The individual was participating in a clinical study evaluating Hympavzi in patients with hemophilia A or B, with or without inhibitors.

In a statement, Pfizer said it is working with the study investigator and an independent external Data Monitoring Committee to gather more information.

The company described the incident as involving “complex, multi-factorial circumstances.”

Hympavzi, a once-weekly injectable therapy, was approved in the United States last year to prevent or reduce bleeding episodes in hemophilia A or B patients aged 12 and older.

The drug works by targeting blood-clotting proteins.

Pfizer said it does not currently anticipate any changes to the drug’s safety profile based on available data and the overall clinical evidence collected to date.

Hemophilia is a genetic disorder in which the body lacks sufficient clotting factors, leading to spontaneous or prolonged bleeding, particularly after injuries or surgery.

Earlier this year, Pfizer announced it would halt global development and commercialization of its hemophilia gene therapy Beqvez, citing limited demand from patients and physicians.

Beqvez had been approved in the U.S. as a one-time treatment for adults with moderate to severe hemophilia B. — Agencies