Bayer sues Sandoz over oral contraceptive drug

FRANKFURT, Aug 5 (Reuters) - Bayer BAYG.DE has filed a patent infringement lawsuit against Sandoz, a unit of Novartis (NOVN.VX) that sought U.S. Food and Drug Administration (FDA) approval for a generic version of oral contraceptive drug YAZ, the German drugmaker said on Tuesday.

A Bayer spokesman declined to give further details. YAZ is the lower dose version of its contraceptive drug Yasmin. Bayer retains FDA marketing exclusivity for YAZ until March next year.

Companies often allege patent infringement when rival drugmakers seek FDA approvals to make a generic version of a patented drug.

In June Bayer agreed to supply a generic version of Yasmin for Barr Pharmaceuticals Inc BRL.N to market in the United States in return for a fixed portion of sales.

Barr had challenged the Yasmin patent held by Bayer and in March a U.S. district court found that the patent held by Bayer was invalid. Bayer has appealed against the ruling.

Bayer has also filed a patent infringement suit against Watson Pharmaceuticals (WPI.N), which has sought FDA approval for a generic version of YAZ.

Yasmin had sales of 321 million euros ($497 million) in the United States alone in 2007. Yasmin and its related products YAZ and Yasminelle posted worldwide sales of 1.04 billion euros last year -- Bayer's largest product family by turnover.

Shares in Bayer were up 1.7 percent at 55.55 euros at 1115 GMT. (Reporting by Frank Siebelt; Writing by Mantik Kusjanto; Editing by Greg Mahlich)