India’s Dr Reddy’s Laboratories has told the country’s leading newspaper it will challenge a US patent infringement suit filed against it by the world’s number one pharmaceutical giant, Pfizer, last month.

Dr Reddy’s is looking to market generic versions of the blockbuster cholesterol lowerer Lipitor (atorvastatin) – the world’s best selling medicine, pulling in annual revenues in the region of $12 billion. Pfizer has already sought to block Dr Reddy’s application to market the 10mg, 20mg and 40mg versions of the drug, while this latest suit concerns the higher dose 80mg version, according to India’s Economic Times

Though Pfizer’s central patent for the crystalline form of atorvastatin expires in July 2016, and it retains paediatric exclusivity through to January 2017, it came to an out of court agreement with Ranbaxy in 2008 that will see the Indian firm sell a low priced version of the enantiomer version of the drug from November this year.

The two firms have been fighting over the validity of patents covering Lipitor all over the world since 2003 and a number of analysts thought that Ranbaxy could possibly launch its generic version of the drug as soon as March 2010 in the USA, when Pfizer’s basic patent was set to expire. The enantiomer patent expires in the USA in 2011, while various process and crystalline form patents are valid until 2016 and 2017.

The cases against Dr Reddy’s have all been filed in the same US Court of Delaware. But if the generics firm is successful, it will be able to launch its copycat versions in the USA from May 2012, when Ranbaxy’s six-month exclusivity expires.  

Third-quarter sales of Lipitor fell 11% to $2.53 billion.