King Pharmaceuticals Research and Development, Inc. along with Astellas US LLC and Astellas Pharma US, Inc. have filed a patent infringement lawsuit in the United States against Sicor Inc., Sicor Pharmaceuticals, Inc., Teva Pharmaceuticals USA, Inc. and Teva Pharmaceutical Industries, Ltd. regarding submission of an abbreviated new drug application for a generic version of Adenoscan (adenosine injection), a pharmacologic stress agent indicated as an adjunct to thallium-201 myocardial perfusion scintigraphy in patients unable to exercise adequately.

The company release states, Astellas is the exclusive licensee of certain rights under King's US patent No. 5,070,877 and has marketed Adenoscan in the US since 1995. The patent infringement action was filed in the US District Court in Delaware on May 26, 2005, requesting, among other things, an order prohibiting approval of Sicor's ANDA prior to the expiration date of the '877 patent. Astellas is also an exclusive licensee under another US patent covering the use of Adenoscan, on which Astellas and the patent holder have also brought suit.

Astellas US LLC and Astellas Pharma US, Inc. are US subsidiaries of Tokyo-based Astellas Pharma Inc., a research-based pharmaceutical company.