Teva Pharmaceutical Industries has launched a generic version of Bayer's big-selling contraceptive Yaz earlier than expected, a move which has seen the German drugmaker file a lawsuit immediately.

The Israeli firm has announced today that it has commercially launched its version of Yaz (drospirenone and ethinyl estradiol) under the brandname Gianvi. As the first company to file an Abbreviated New Drug Application for this product, Teva says it has been awarded a 180-day period of marketing exclusivity, having received approval from the US Food and Drug Administration last month.

Despite getting the thumbs-up for Gianvi from the FDA, the timing of the launch has caught observers on the hop, seeing as how an agreement had previously been reached between the firms to let Teva unit Barr Pharmaceuticals launch an authorised generic, supplied by Bayer, in July 2011. Analysts at Deutsche Bank issued a research note expressing their surprise, noting that the Leverkusen-headquartered group could lose 200 million euros in 2010 sales and 250 million euros in 2011.

Bayer responded by filing a lawsuit, saying it believes that Teva’s decision constitutes an act of infringement on intellectual property. The company is already suing Watson Pharmaceuticals and Novartis’ Sandoz division.

Teva noted that sales of Yaz reached $782 million in the USA for the year ended December 31, 2009, However, for the first quarter, the Yaz/Yasmin/Yasminelle franchise suffered a 10.2% sales decline to 287 million euros. That fall was due to demand in the USA suffering particularly from “the discussion surrounding the thrombosis risk of contraceptives containing drospirenone”, Bayer noted at the time.