FRAZER, Pa. AP _ Biotechnology company Cephalon Inc. said Wednesday it is suing several generic drug developers over patent claims to its extended-release muscle-relaxant Amrix.

Cephalon and Dutch partner Eurand Inc. filed the lawsuit in U.S. District Court in Delaware against Mylan Inc. and Barr Pharmaceuticals Inc. after those companies asked the Food and Drug Administration for approval of generic versions of Amrix.