Endo Pharmaceuticals Inc., a subsidiary of Endo Pharmaceuticals Holdings Inc, and Penwest Pharmaceuticals Co. announced that they have filed a lawsuit against Impax Laboratories, Inc. in the United States District Court for the District of Delaware in connection with Impax's Abbreviated New Drug Application (ANDA) for Opana ER (oxymorphone HCl) extended-release tablets CII, which Impax has announced was rescinded by the FDA.

The lawsuit is in response to a series of Paragraph IV Certification Notices that Endo and Penwest assert were wrongfully served by Impax on Endo and Penwest. These Notices advised that Impax had submitted to the FDA an ANDA seeking approval to market generic versions of all four dosage strengths of Opana ER.

The lawsuit against Impax not only alleges infringement of certain Orange Book-listed US patents that cover the Opana ER formulation, but also seeks declaratory judgment that, among other things, Impax has no legitimate basis to trigger the Hatch-Waxman ANDA patent litigation process because the FDA, according to Impax, has rescinded its acceptance of Impax's ANDA. It further asks the court to declare that the Paragraph IV Certification Notices that Impax served on Endo and Penwest are null, void and of no legal effect.

Opana ER has been granted new dosage form regulatory exclusivity that prevents the FDA from approving any ANDA for a generic version of Opana ER for launch prior to June 22, 2009, the date such regulatory exclusivity expires.

Endo Pharmaceuticals Holdings Inc. is a fully integrated specialty pharmaceutical company with market leadership in pain management products. Through its Endo Pharmaceuticals Inc. subsidiary, the company researches, develops, produces and markets a broad product offering of both branded and generic pharmaceuticals, meeting the needs of healthcare professionals and consumers alike.

Penwest is a drug development pharmaceutical company dedicated to bringing to the marketplace innovative products that help improve the lives of patients. The company's goal is to identify, develop and commercialise prescription products that address unmet medical needs, primarily for diseases of the nervous system. Penwest is currently applying its drug delivery and drug development expertise to a pipeline of potential products that are in various stages of development and that it intends to commercialise independently or through third party alliances.