Law360 (April 21, 2021, 6:30 PM EDT) — Endo Pharmaceuticals Inc. and Impax Laboratories Inc. told an Illinois federal court that buyers who say they overpaid for Opana ER have to show more than the Federal Trade Commission did when it secured a Fifth Circuit win last week over the alleged delay of generic versions of the drug.

Endo and Impax responded Tuesday to a notice of supplemental authority lodged by the buyers that pointed to the Fifth Circuit’s April 13 decision upholding the commission’s findings that Impax violated antitrust law through a deal to delay its generic version of Endo’s prescription painkiller.

The response contended the appellate ruling…