AstraZeneca has entered into a new supply and distribution agreement with Par Pharmaceutical to distribute an authorized generic version of metoprolol succinate in the United States. Under the arrangement, AstraZeneca will continue to market its branded version of metoprolol succinate, Toprol-XL, throughout the United States.

At least initially, the generic version will be available only in the 25-mg dosage—a strength that represents an estimated 20% of AstraZeneca's Toprol-XL sales in the United States. The agreement between AstraZeneca and Par was announced on the heels of the US launch of a 25-mg version of metoprolol succinate by Sandoz'Eon Labs.

Although patent protection for Toprol-XL does not expire until September 2007, a federal district court declared that patent invalid last year, a ruling that paved the way for Eon's generic version.