Dr Reddy's Laboratories said on Monday it has filed a suit against Pfizer Inc. to enable it to market a generic version of Pfizer's blockbuster antidepressant Zoloft.

The company, based in Hyderabad, said it filed a lawsuit in the District Court for the District of New Jersey claiming that it should be permitted to sell its proposed copycat version of Zoloft in the United States.

Dr Reddy's said it is already seeking marketing approval from the U.S. Food and Drug Administration to sell the copycat, and has filed a challenge to four of Pfizer's five key patents over Zoloft.

But Pfizer has not sued Dr Reddy's within the 45-day period after Dr Reddy's officially filed with the US FDA an application to market a generic version of a drug that is normally permitted to branded companies when faced with a generic challenge.

Pfizer, the world's largest drugmaker, has said that its 2003 earnings per share goal of about $1.80 assumes that none of its major drugs will face cheaper generic competition. But anti-convulsant Neurontin, hypertension drug Norvasc and Zoloft are all subject to court battles over potential copycats or altered versions.