UPDATE 1-U.S. FDA approves migraine drug from Glaxo, Pozen

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WASHINGTON, April 15 (Reuters) - The U.S. Food and Drug Administration has approved a combination migraine drug from GlaxoSmithKline Plc (GSK.L: Quote, Profile, Research, Stock Buzz) (GSK.N: Quote, Profile, Research, Stock Buzz) and Pozen Inc (POZN.O: Quote, Profile, Research, Stock Buzz), the companies said on Tuesday.

The drug, Treximet, is expected to be available in U.S. pharmacies by the middle of May, the companies said.

The two-in-one drug has faced repeated delays since Pozen sought U.S. approval in 2005. FDA officials had earlier expressed concern over heart safety and the risk of gene toxicity, asking for more data.

The drug combines common painkiller naproxen with Glaxo's Imitrex, the most widely used drug in the lucrative triptan class of migraine drugs. The duo aims to act faster and last longer by targeting different pathways in the brain.

Last August, the FDA asked the drugmakers for more data after a preclinical study pointed to possible chromosomal risks. In January, Pozen said a study found no genetic abnormalities.

Investors have been anxious for an approval decision since then, with some analysts cutting sales forecasts. Others have been more positive, citing the drug's combination advantage.

At issue is how much the repeated delays have hurt the drugmakers' ability to switch patients to Treximet, formerly known as Trexima, before cheaper generic versions of Imitrex become available in late 2008.

Shares of GlaxoSmithKline fell 0.3 percent to close at $42.41 on Tuesday, while Pozen's shares rose about 6.4 percent to $10.53. (Reporting by Susan Heavey in Washington, with additional reporting by Justin Grant in New York; Editing by Braden Reddall)