Bayer is suing Novartis' Sandoz unit in a bid to stop the latter from marketing a generic version of the German drugmaker’s oral contraceptive Yaz.

Sandoz is looking to get US Food and Drug Administration approval to sell its version of Yaz (drospirenone and ethinyl estradiol) and in its application to the agency claims that Bayer’s patents are invalid. However, the Leverkusen-based firm disagrees and has filed identical suits in Denver and Las Vegas. The case will be heard in one of those cities and Bayer will ask the judge to block any approval until two patents on Yaz expire in 2014.

The suits against Sandoz are part of Bayer’s battle to defend its Yasmin range of contraceptives to which Yaz belongs. The problems started in March when a court in New Jersey declared the key patent on Yasmin (also drospirenone and ethinyl estradiol) invalid.

This prompted Bayer to sign an agreement with Barr Pharmaceuticals in June to supply the latter with copycat, but authorised, versions of Yasmin now and for Yaz as well (by July 2011). However Bayer is continuing with a patent dispute with Barr over Yaz.

Second-quarter sales of the Yasmin franchise climbed 22.0% to 305 million euros and Bayer is also involved in litigation with Watson Pharmaceuticals over the latter’s attempts to file its versions of Yasmin and Yaz with the FDA.