A federal appeals court has ruled that drug manufacturer Actavis’ attempted switch of patented Alzheimer’s medication, which halted distribution of the old drug before its patent expires this summer, violates U.S. antitrust law.

The decision unsealed Wednesday explains the ruling by a three-judge panel of the U.S. Court of Appeals for the Second Circuit that requires the Irish company to keep distributing Namenda until 30 days after its patent expires on July 11.