Ending nearly three years of litigation, drug firm Dr Reddy's Laboratories has entered into

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a patent suit settlement agreement with Pfizer over the latter's cholesterol lowering drug 'Lipitor'.

In a statement, Dr Reddy's Laboratories said the settlement with Pfizer is for resolving litigation related to Lipitor tablets of strengths 10 mg, 20 mg, 40 mg, and 80 mg, known generically as atorvastatin calcium tablets.

"The terms of the agreement are confidential, and the agreement itself is subject to review by the US Department of Justice and the Federal Trade Commission," the Hyderabad-based firm said.

In December 2009, Pfizer had moved to the US District Court for the District of Delaware against Dr Reddy's Laboratories Ltd and Dr Reddy's Laboratories Inc for infringement of Pfizer's crystalline atorvastatin patent.

Pfizer had stated that the Indian firm's plans to launch a generic version of the world's best-selling medicine will infringe upon its patent.

DRL had filed an abbreviated new drug application (ANDA) with the US Food and Drug Administration seeking approval to market an 80 mg dosage strength of atorvastatin calcium.

Pfizer's patent on Lipitor expires in July 2016 and has pediatric exclusivity though January 2017. Lipitor gets about USD 12 billion in annual sales for Pfizer.

In June 2008, Pfizer settled for an out-of-court agreement with Daiichi Sankyo-owned Ranbaxy, allowing it to sell a low-priced version of the medicine from November 2011, when one of its key patents on the same drug expires.

Ranbaxy now holds a six-month marketing exclusivity for its low-cost version of the product, as it was the first generic drug maker to challenge Pfizer's patent for Lipitor.