The U.S. Food and Drug Administration approved Bayer AG's therapy for the most common form hemophilia, the company said on Thursday, about three weeks after the treatment was cleared for use in Europe.

The therapy, Kovaltry, is designed to reduce bleeding in patients with hemophilia A when infused prophylactically two or three times per week, and was approved by the European Commission on Feb. 22. 

Due to a fault in a gene that regulates the body's clotting mechanism, people with hemophilia are susceptible to spontaneous bleeding as well as severe bleeding following injuries or surgery.

Hemophilia has no cure. Patients typically require frequent injections of blood clotting proteins that can cost up to $300,000 a year for a single patient.

A Bayer spokeswoman said the company could not specify a price for Kovaltry but added that it had already captured the second-largest share of the hemophilia A market in the United States.

The German drugmaker's established hemophilia A therapy, Kogenate, brought in global sales of about 1.15 billion euros ($1.30 billion) last year.

Kovaltry will enter a crowded market. Existing products with varying dosing schedules include those from Baxalta Inc, which is being acquired by Shire Plc, Pfizer Inc, Biogen Inc and Novo Nordisk A/S.

But more convenient therapies, perhaps once-monthly regimens, from Roche Holding AG and Alnylam Pharmaceuticals Inc could reach the market as early as 2017, Morningstar analysts wrote in a note last month.

Since the faulty gene is carried on the X chromosome, hemophilia is almost entirely a disease of men, and affects about 20,000 Americans. Bayer estimates there are currently about 16,000 people living with hemophilia A in the United States.

"We have found that many hemophilia A patients are comfortable with their existing treatment, but there are always early adopters interested in new therapies," said Olubunmi Afonja, Bayer's director of medical affairs for hematology.

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About 75 percent of the estimated 400,000 hemophiliacs around the world still receive inadequate treatment or have no access to therapy, according to the U.S.-based National Hemophilia Foundation.

Bayer, among others, is also exploring the use of gene therapy in hemophilia, which aims to achieve a cure by fixing the gene responsible for the largely inherited disorder. The company has tied up with U.S. biotech firm Dimension Therapeutics to develop such a therapy for hemophilia A.

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