UPDATE 1-Court says Astra's Prilosec patent infringed

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WASHINGTON, Aug 20 (Reuters) - A U.S. appeals court upheld an infringement finding against generic drug makers Apotex and Impax on Wednesday in a case brought by AstraZeneca (AZN.L) to defend the patents for its popular heartburn drug Prilosec.

AstraZeneca, one of the world's biggest drugmakers, prevailed in the case before the U.S. Court of Appeals for the Federal Circuit on Wednesday. It lost an appeal in June which allowed another generic firm, Mylan MYL.N, to sell a copycat version of Prilosec, which used to be the biggest selling drug in the world.

The generic is sold as omeprazole, the active ingredient in Prilosec.

The litigation began in 2000, when Astra sued several companies that had filed applications with the Food and Drug Administration to make a generic Prilosec.

Mylan, which began selling a generic Prilosec in August 2003, was part of that group, as were Apotex and Impax.

The U.S. District Court for the Southern District of New York had ruled that Mylan did not infringe on Astra's patents for omeprazole but that Apotex and Impax did infringe.

The Federal Circuit upheld the Mylan decision in June 2008 and the Apotex and Impax decision on Wednesday.

(Reporting by Diane Bartz; Editing by Tim Dobbyn, Phil Berlowitz)