GlaxoSmithKline (NYSE:GSK) is taking two drugs companies to court claiming that their efforts to launch generic versions of enlarged prostate drugs Avodart and Jalyn infringe on GSK patents.

GSK said in the suit that abbreviated new drug applications filed with the Food and Drug Administration by Mylan (Nasdaq: MYL) and Impax Laboratories (Nasdaq: IPXL) will violate three patents for its prostate treatments. GSK filed the patent infringement lawsuit on Sept. 8 in the U.S. District Court for the District of Delaware.

Avodart’s 2010 sales eclipsed $900 million for London-based GSK, which has its U.S. headquarters in Research Triangle Park. The drug was approved by the FDA in 2001 to treat patients with symptomatic benign prostatic hyperplasia, or BPH, known more simply as an enlarged prostate. Avodart blocks enzymes that promote prostate growth. It also shrinks the prostate, relieving symptoms such as frequent and difficult urination. Avodart’s U.S. patent expires in 2015.

Jalyn was approved in June 2010 as another BPH treatment. The combination drug pairs GSK’s Avodart with another drug called tamsulosin. While Avodart treats BPH symptoms and shrinks the prostate over time tamsulosin treats the signs and symptoms of BPH and works by relaxing the muscles in the bladder and prostate. According to figures from IMS Health, Jalyn had U.S. sales of more than $30 milllion for the 12 months ending May 31. Avodart’s first patent expires next September.

According to GSK’s complaint, Mylan has applied to market a generic version of Avodart; Impax plans a generic for Jalyn. With patent expirations on Avodart and Jalyn approaching, the two drugs are becoming more prominent targets for generic competitors. Last winter, Anchen Pharmaceuticals filed its application with the FDA for marketing approval on its versions of Avodart and Jalyn. GSK is suing to block Anchen.

Jalyn also faces a generic challenge from Watson Pharmaceuticals (NYSE:WPI), which in July filed with the FDA an application to market its version of the drug. GSK has filed a separate suit against Watson in federal court in Delaware to block the Watson generic.

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