Barr Pharmaceuticals, Inc confirmed that its subsidiary, Barr Laboratories, Inc, has initiated a challenge of the patents listed by Endo Pharmaceuticals Inc in connection with its Opana ER (oxymorphone hydrochloride) extended-release tablets, 5 mg, 10 mg, 20 mg and 40 mg.

Barr filed its Abbreviated New Drug Application (ANDA) containing a paragraph IV certification for a generic version of Opana ER with the US Food & Drug Administration (FDA), and following receipt of the notice from the FDA that Barr's ANDA had been accepted for filing, Barr notified the New Drug Application (NDA) and patent holder.

On October 20, 2008, Endo Pharmaceuticals Inc and Penwest Pharmaceuticals Co filed suit in the US District Court for the District of Delaware to prevent Barr from proceeding with the commercialization of its product. This action formally initiates the patent challenge process under the Hatch-Waxman Act.

Opana ER (oxymorphone hydrochloride) extended-release tablets, 5 mg, 10 mg, 20 mg and 40 mg had annual sales of approximately $130 million in the US, based on IMS sales data ending August 2008.