Eli Lilly and Company, the US-based multinational pharmaceutical major, has sued Sun Pharmaceuticals in the US, alleging the company infringed its patent on Gemzar, a blockbuster cancer drug.

The suit, filed with the Southern District of Indiana, is in response to Sun's abbreviated new drugs application filed with the US Food and Drug Administration in October 2006 seeking approval for a generic process to manufacture the drug Gemcitabine.

While Eli Lilly's basic patent on the active pharmaceutical ingredient Gemcitabine hydrochloride will expire on November 15, 2010,  another patent on the method to manufacture the drug is valid until 2013. Sun Pharma claimed that the 2013 patent is invalid.

"Sun Pharma is confident in our approach to challenge that patent with Para IV certification. We hope to win the litigation and launch the product in the US market" said Uday Baldota, vice president, international relations, Sun Pharma.

Gemzar, a commonly used cancer drug to treat non-small cell lung cancer, pancreatic, bladder and breast cancer, is one among the top selling drugs of Eli Lilly. The drug had worldwide sales of $1.408 billion in 2006, including sales worth $609.8 million coming from the US market. 

Sources said Eli Lilly had earlier sued Sicor Pharmaceuticals, a subsidiary of Teva of Israel and Mayne Pharma of Australia during last year for filing ANDAs challenging the 2010 and 2013 patents on Gemzar.

In February 2006, Eli Lilly filed a lawsuit against Sicor in the US District Court for the Southern District of Indiana, and in response, Sicor filed a declaratory judgment action in the US District Court for the Central District of California demanding to dismiss the suit, asserting the Indiana court lacks jurisdiction. However, the California court dismissed that case.

In September 2006, Mayne Pharma (USA) Inc. filed a similar ANDA for Gemzar and in October 2006, Eli Lilly filed a lawsuit against Mayne in the Southern District of Indiana in response to the ANDA filing. In response, Mayne filed a lawsuit claiming the Indiana court lacks jurisdiction. 

Patent experts said the litigations initiated by Eli Lilly will prevent launch of any generic versions of Gemzar by another 30 months, as per the US patent rules.

It may be noted that Sun Pharma's US subsidiary Caraco Pharmaceuticals recently had filed a case with the US District Court for the Eastern District of Michigan against Forest Laboratories Inc. of US and Lundbeck A/S of Denmark, demanding to allow launch of its generic version of anxiety and depression drug Lexapro, known generically as escitalopram oxalate.

Sun Pharma's share prices went up by over 4 per cent on Friday to Rs 1058.80 from the previous day close of Rs 1017.25 in the Bombay Stock Exchange.