Astellas sues Impax over generic version of Flomax

TOKYO, July 22 (Reuters) - Astellas Pharma Inc (4503.T) said on Tuesday it had filed a suit against unlisted Impax Laboratories Inc over the U.S. company's application for a generic version of Japanese drug maker's prostate drug Flomax.

Astellas and Germany's Boehringer Ingelheim Pharmaceuticals Inc, which co-promotes Flomax in the United States, jointly filed the suit at the U.S. District Court, Northern District of California on Friday.

Flomax, one of Astellas' mainstay drugs, is used to treat urinary problems in men from enlarged prostates. (Reporting by Yumiko Nishitani)