Watson Pharmaceuticals, Inc., a leading specialty pharmaceutical company, confirmed that its subsidiary, Watson Laboratories, Inc., has been sued by Endo Pharmaceuticals Inc. and Penwest Pharmaceuticals Co. in connection with the filing of Watson's Abbreviated New Drug Application (ANDA) for oxymorphone hydrochloride Extended-Release tablets, 40mg.

Watson's oxymorphone hydrochloride Extended-Release tablets product is a generic version of Endo's Opana ER which is indicated for the relief of moderate to severe pain in patients requiring continuous, around-the-clock opioid treatment for an extended period of time. Opana ER had approximately $245 million in brand sales for the twelve months ending December 31, 2009, according to IMS Health.

On January 19, 2010, pursuant to the Hatch-Waxman Act, Watson notified Endo and Penwest that its ANDA contained a paragraph IV certification asserting that US Patent Nos. 5,662,933, 5,958,456, and 7,276,250, which are listed in the Orange Book for Opana ER, are invalid, unenforceable and/or not infringed.