Generic-drug maker Mylan Inc. (MYL) has sued the U.S. Food and Drug Administration in an effort to allow the introduction of generic versions of Pfizer Inc.'s (PFE) popular cholesterol-lowering drug Lipitor in June, five months earlier than expected.

Mylan wants a federal judge to force the FDA to deny an application by rival Ranbaxy Laboratories Ltd. (500359.BY) to sell generic Lipitor, and to deny Ranbaxy a six-month period of market exclusivity for the copycat product following its anticipated introduction in November. Mylan filed its lawsuit in federal court in Washington on Friday.

Ranbaxy has been expecting a six-month exclusivity period because it was the first to file for FDA approval of a generic version of Lipitor several years ago. Also, Ranbaxy agreed to wait until Nov. 30 to launch its generic product as part of a 2008 settlement of long-running patent litigation with Pfizer.

But questions have been mounting about whether Ranbaxy will be in a position to sell generic Lipitor in November, and Mylan's lawsuit further clouds the picture.

The FDA has cited Ranbaxy for manufacturing deficiencies at plants in India, and has accused the company of providing falsified data and test results in drug applications to the agency.

Mylan claims in its lawsuit that Ranbaxy has engaged in a pattern of submitting drug applications to the FDA containing false and unreliable data regarding a Ranbaxy manufacturing plant in India. Mylan accused the FDA of failing to enforce its "application integrity policy" against Ranbaxy, which Mylan says should result in denial of Ranbaxy's application to market generic Lipitor.

Mylan says generic versions of Lipitor should be allowed to enter the market in June because that is when Pfizer's exclusivity associated with one of the patents for Lipitor expires.

"We believe the FDA has all the information its needs to decide today on Ranbaxy's 180-day exclusivity," said Mylan spokeswoman Nina Devlin. She said the company couldn't comment further on the litigation.

FDA spokeswoman Sandy Walsh said the agency doesn't comment on lawsuits.

Spokesmen for Pfizer and Ranbaxy couldn't immediately be reached.

Lipitor is the top-selling drug in the world, generating global sales of $10.7 billion for 2010, $5.3 billion of which came from the U.S.

In its lawsuit, Mylan estimated consumers and insurers could save between $10.9 million and $18.6 million per day when generic Lipitor becomes available by paying lower prices for the generic versions.

Pfizer has granted Watson Laboratories Inc. (WPI) a license to sell what is known as an authorized-generic version of Lipitor beginning in November; Pfizer will supply the product.

Mylan had previously challenged the validity of patents for Lipitor in an effort to sell a generic version of the drug. Litigation arising from the challenge was settled in January on confidential terms, according to Pfizer's annual report.

Under federal law, the first successful generic challenger is awarded a 180-day exclusivity period from when it launches, but regulatory and manufacturing issues at Ranbaxy may delay an approval. If that occurred, barring a decision favorable to Mylan in its new lawsuit, other generic manufacturers may be blocked from selling a generic version of Lipitor until Ranbaxy's exclusivity expired, leaving Watson as the sole generic supplier beginning in November.

Pfizer has also settled Lipitor patent litigation with Teva Pharmaceutical Industries Ltd. (TEVA) and analysts have generally expected Teva to begin selling its generic version in mid-2012, at the same time Mylan had been expected to launch.

-By Peter Loftus, Dow Jones Newswires; 1-215-982-5581; peter.loftus@dowjones.com