A group of retailers isn’t giving up its fight against pharmaceutical companies that they claim are engaging in anti-competitive practices.

Yesterday, five retailers—Walgreen Co., Kroger Co., Safeway Inc., SuperValu Inc. and HEB Grocery Co.—sued Pfizer Inc. and generic-drug manufacturer Ranbaxy Laboratories Ltd. for allegedly conspiring to stall sales of competing generic versions of Pfizer’s best-selling drug, Lipitor, which treats high cholesterol.

According to the lawsuit, Pfizer and India-based Ranbaxy kept other generic versions of Lipitor off the market until Nov. 30, 2011, which was almost two years after the original patent on the drug expired. The plaintiffs say the two pharmaceutical companies did this by obtaining a fraudulent patent, fabricating litigation, entering a price-fixing agreement to stall other cheaper generics from entering the market and entering agreements with pharmacy benefit managers that forced retailers to purchase more Lipitor.

The retailers say the scheme forced them to pay “hundreds of millions of dollars more” for the drug than they would have paid if they had been able to purchase generics.

The suit comes on the heels of another one that many of the same retailers filed against Pfizer and generic manufacturer Teva Pharmaceutical Industries Ltd. in November 2011. In that suit, the plaintiffs accused the drug makers of conspiring to keep generic versions of Pfizer’s antidepressant Effexor XR off the market. Two more retailers—CVS Caremark Corp. and Rite Aid Corp.—filed a similar antitrust lawsuit in June.

Read Thomson Reuters for more about the retailers’ latest lawsuit against Pfizer.

For more InsideCounsel stories about legal concerns surrounding generic drugs, read:

CVS, Rite Aid sue Pfizer, Teva over antidepressant

Court denies AstraZeneca’s bid to block generic Seroquel

Judges dismiss cases against generic-drug makers in droves

Glaxo has right to sell generic Paxil

Walgreens and Par Pharmaceuticals accused of overcharging for meds

Retailers claim Pfizer kept generic drug off the market

Generic drugmakers accused in Medicaid scheme

Supreme Court delivers big win to generic-drug makers

Pfizer victorious in challenge to Viagra patent