Dec 23 (Reuters) - A patient who was being treated with Pfizer's PFE.N hemophilia drug, Hympavzi, as part of a long-term study died after experiencing serious side effects, the company said.

The individual died on December 14 after suffering a stroke followed by a brain hemorrhage, according to the European Haemophilia Consortium, a patient support group.

The patient was enrolled in a study that was testing Hympavzi in patients with hemophilia A or B with or without inhibitors.

"Pfizer, together with the trial investigator and the independent external Data Monitoring Committee, are actively gathering information to better understand the complex, multi-factorial circumstances surrounding this occurrence," the company said in a statement.

The therapy, a once-a-week injection, gained U.S. approval last year to prevent or reduce bleeding episodes in hemophilia A or B patients aged 12 years and older by targeting blood-clotting proteins.

Pfizer does not anticipate any impact to safety for patients treated with the drug based on its current knowledge and the overall clinical data collected to date, the company said.

People with hemophilia have a defect in a gene that regulates the production of proteins called clotting factors, causing spontaneous and severe bleeding following injuries or surgery.

Earlier this year, Pfizer said it would halt global development and commercialization of its hemophilia gene therapy, Beqvez, citing soft demand from patients and their doctors.

Beqvez, a one-time therapy, was approved in the U.S. for the treatment of adults with moderate to severe hemophilia B.

(Reporting by Sneha S K in Bengaluru; Editing by Anil D'Silva)

((Sneha.SK@thomsonreuters.com;))