AstraZeneca on Wednesday announced that it had filed separate patent infringement actions in the United States District Court, Delaware, against seven generic drug manufacturers, which have submitted abbreviated new drug applications (ANDAs) with the US Food and Drug Administration (FDA) seeking marketing authorisation for Crestor.

Cobalt Pharmaceuticals was the first to challenge the patent on Crestor among the top-selling cholesterol-reducing drugs such as Pfizer's [Get Quote] Lipitor and Schering Plough's Zetia. The main US patent for Crestor is valid until January 2016.

The worldwide sales of Crestor touched $2 billion in 2006. The drug recorded US sales of $696 million in the first half of 2007 and has posted third quarter worldwide sales of $691 million.

AstraZeneca said it did not file patent infringement suit against Glenmark since the company did not notify intention to market its generic version prior to the expiration of the patent, which covers the active ingredient and expires in 2016.

According to the US rules, when a generic company challenges the patent of an innovator's drug by filing a Para IV ANDA, that has to be officially informed to the innovator.

The innovator then has to sue the challenger and that entails a 30-month stay on approving the marketing applications by the FDA. AstraZeneca spared Glenmark and Teva from legal action, as both these companies did not challenge the main patent.

Leading generics companies such as Teva, Par Pharma, Apotex, Mylan and Novartis's [Get Quote] generics company Sandoz are the other contenders for the drug.

Analysts pointed out that, surprisingly, leading Indian generics companies, Ranbaxy [Get Quote] and Dr Reddy's, had so far not entered the fray for this blockbuster drug.