By Bill Berkrot

May 12 (Reuters) - Biogen Idec Inc and partner Swedish Orphan Biovitrum AB on Monday said they will donate hemophilia drugs for use in developing nations in quantities large enough to treat tens of thousands of patients over the next decade.

The potentially life-saving clotting factor medicines would be intended for use in Africa, Asia and elsewhere, where three quarters of the world's 400,000 hemophilia sufferers have limited or no access to such drugs, and where most fail to live into adulthood as a result.

Biogen and Sobi announced their intention to donate one billion international units of clotting factor drugs over 10 years at the World Federation of Hemophilia (WFH) meeting in Melbourne, Australia.

"WFH do their work in countries that consume less than 1 iu per capita. That's a level below which people are dying, where they don't even have enough to treat the life-threatening bleeds," Paula Cobb, Biogen's head of hematology, said in a telephone interview.

Hemophilia, an inherited disorder in which the blood does not clot properly, is a new therapeutic area for Biogen. The companies last month received U.S. approval for Alprolix, which treats the more rare hemophilia B.

The success of the humanitarian effort will hinge on Food and Drug Administration approval of Eloctate for hemophilia A, which would account for at least 85 percent of the donated product. That approval is expected later this year.

Biogen, based in Weston, Massachusetts and Stockholm-based Sobi initially committed to donate up to 500 million units to WFH over five years. The remaining 500 million units will be made available for future distribution.

The drugs would primarily be used for emergency treatments rather than preventive care as is common in the developed world, where a year of treatment can cost upwards of $300,000.

The quantity of donated product would enable doctors to treat more than 75,000 joint bleeding episodes, more than 2,000 life-threatening bleeds and to perform thousands of surgical procedures that would not be possible without access to clotting drugs, the companies said.

"We wanted to do something significant that would change and really shift the way donation programs in that field will work," said John Cox, Biogen's head of manufacturing and supply. He added that he hopes other companies would be prompted follow suit.

It was not possible to put a commercial value on the donation as Biogen has yet to set a price for Eloctate. Alprolix was priced at $2.85 per unit. "It is tens of millions of dollars in terms of internal manufacturing supply and cost," Cox said.

Drugmakers, under pressure from the international community over the high prices of their medicines, have sought to burnish their images by offering HIV drugs and other medicines at drastically reduced cost in Africa and poor nations in other regions. Biogen officials said they were responding to a plea for help from the WFH.

"Trying to price this for the developing world was not part of the conversation. When we sat down with the executive team, it was not a public relations discussion," Cox said.

(Reporting by Bill Berkrot in New York; Editing by Eric Walsh)