Impax Labs will pay $20 million to settle claims it kept its generic acne drug off the market in a “pay-for-delay” deal.

The plaintiffs, a class of retailers including Rite Aid and CVS, claimed that in 2008, Impax settled a complaint against Medicis Pharmaceutical — alleging the other drugmaker’s patent on its drug Solodyn (minocycline hydrochloride) was invalid — for $40 million and agreed to delay the generic until 2011.

The company has already agreed to pay $35 million to settle pay-for-delay claims over Solodyn brought by a class of direct purchasers.