A US court has ruled against a patent for Bayer's oral contraceptive Yasmin, one of its most profitable products, the German pharmaceutical and chemicals group said.Bayer disagrees with the court's decision and will consider its legal options in this regard.

A US district court in New Jersey ruled in favour of a patent challenge by Barr Pharmaceuticals, allowing its subsidiary Barr Laboratories to sell a version of Yasmin in the United States.

The ruling was another blow for Bayer, the maker of Aspirin, and its share price lost 3.92 percent to 48.23 euros in early trade, leading losers on the Frankfurt stock exchange which was flat overall.

Yasmin is part of a group of oral contraceptives along with YAZ and Yasminelle that were Bayer's best-selling pharmaceutical products in 2007, generating revenues of 1.04 billion euros (1.58 billion dollars). Regardless of the court decision, Bayer will have US market exclusivity for YAZ until March 2009, it said.

But the group lowered the 2008 profit margin target for its health care unit and now expects it to widen "toward" 27 percent from 25.6 percent in 2007, the statement said.

The US ruling came after Bayer was forced to halt sales of its anti-bleeding drug Trasylol, an unfavourable study regarding use of its Betaferon treatment for multiple sclerosis and a complaint by the drug group Novartis against the Bayer drug Kogenate, used to treat haemophilia.

Finally, phase three tests of Nexavar, its future "blockbuster" treatment for lung cancer, ended in failure. In 2007, Bayer posted record net profit of 4.7 billion euros on sales of 32 billion, in large part stemming from its pharmaceutical division.