The world's largest generic drug maker, Teva, last week asked a U.S. court to resolve a dispute over its unexpectedly swift introduction to the U.S. of a generic version of Bayer's YAZ birth control pill.

Bayer Schering Pharma said that it had filed a patent infringement lawsuit against Israel's Teva Pharmaceutical Industries Ltd after Teva launched the contraceptive under the brand name Gianvi. Teva brought the drug to U.S. markets on May 28, earlier than the July 2011 introduction the drugmakers had previously agreed upon, unless other generics makers managed to enter the market earlier. The generic product was approved by the U.S. Food and Drug Administration on March 30, 2009.

In a request for a declaratory judgment filed in Manhattan federal court on Wednesday, Teva contended that its "launch of a generic formulation of the YAZ product infringes no valid patent claim.

"There is, therefore, a dispute between Bayer and plaintiffs that is definite and concrete, that requires the resolution of specific factual and legal issues as to which Bayer and plaintiffs take different views, and that admits of specific relief through a judgment of a conclusive character," Teva's filing in court said.

Barr Laboratories, a wholly owned subsidiary of Teva, was also named as a plaintiff. Teva says YAZ generated sales of $782 million in the U.S. in 2009, citing data from market researcher IMS, and adding it had won a 180-day period of marketing exclusivity. Bayer had previously lost a legal tussle with Teva over the right to sell copycat versions of its bestselling Yasmin and YAZ pills in the U.S.

But Bayer in 2008 agreed to supply the pills to Teva in exchange for royalty payments, cutting its losses from cheaper competition.