Five large drug and grocery chains are suing Pfizer Inc. and a second drugmaker, alleging they conspired to delay sales of cheap generic versions of the blockbuster cholesterol drug Lipitor.

Lipitor, the world's top-selling drug ever, got U.S. generic competition on Nov. 30.

A lawsuit filed by Walgreen Co., the Kroger Co. and three other retailers claims generics should have been available nearly two years earlier, when Lipitor's original patent expired.

The lawsuit accuses Pfizer of patent fraud as well as "illegal, anti-competitive conduct" with generic drugmaker Ranbaxy Laboratories to block other generic drugmakers from selling versions of Lipitor until recently. The suit also accuses Pfizer of making deals with prescription benefit managers to limit sales of generic Lipitor.

Pfizer denies the claims and says it will fight the lawsuit. Ranbaxy declined comment.