In a move that could stop Ranbaxy Laboratories Ltd from marketing the generic versions of Lipitor and Caduet, Pfizer lodged a judgement suit claiming Ranbaxy's proposed generic would infringe two patents related to atorvastatin, the active ingredient in Lipitor.

The cholesterol drug Lipitor is the world's best-selling medicine, which brought in $12.7 billion in 2007, about 26 per cent of Pfizer's total, but faces generic competition in March 2010.

According to lawsuits filed yesterday in federal court in Wilmington, Delaware, Pfizer is seeking a court order barring Ranbaxy from selling a generic version of the medicines until two patents on a process to make the drugs expire in 2016.

The new lawsuits seek to extend the already existing ban on Ranbaxy from selling the generic versions of Lipitor and Caduet until a patent expires in 2010.