Walgreen Co., the biggest U.S. drugstore chain, teamed with Kroger Co., the largest U.S. grocery chain, to accuse Endo Health Solutions Inc. and Impax Laboratories of conspiring to delay the introduction of lower-cost versions of an opioid painkiller.

Walgreen, Kroger, and three other grocery chains - Safeway Inc., HEB Grocery Co., and Albertson's L.L.C. - filed an antitrust suit Friday in federal court in Chicago over delays in the rollout of generic alternatives to Opana ER. The suit joins 11 others against units of Endo International P.L.C.

Endo is officially based in Dublin, Ireland, but its executives work from Malvern, Montgomery County. Impax is headquartered in Hayward, Calif., and has facilities in Philadelphia and Chalfont, Bucks County.

The chains say in their complaint that "Endo paid Impax more than $112 million in cash in exchange for Impax's agreement to delay the launch of its less-expensive generic versions of Opana ER for 21/2 years."

Endo used the extra time to shift consumers to a crush-resistant version of Opana ER that makes abuse of the opioid more difficult, according to the complaint. Walgreen and the grocery chains said they paid millions of dollars in overcharges because of the delay.

Heather Zoumas-Lubeski, a spokeswoman for Endo, declined to comment on the suit. Mark Donohue, a spokesman for Impax, did not immediately return phone and e-mail requests for comment.

The cases have been consolidated before a federal judge. Other cases were brought by unions, an insurer, and drug-purchasing cooperatives. Some of those suing said they paid too much for the painkiller because of the delay.

In related news, the U.S. Food and Drug Administration released new guidelines Wednesday morning designed to help drugmakers create tamper-resistant opioid painkillers that will be more difficult to misuse.

Opioid painkillers are very addictive and have surpassed heroin and cocaine as causes of accidental death in the United States.