Merck is appealing a Delaware federal court ruling that rejected its patent infringement claims against a rival drugmaker, which is planning to sell a generic version of NuvaRing.

U.S. District Judge Gregory M. Sleet of the District of Delaware on Aug. 26 said Merck’s claims under its patent for the popular contraceptive were obvious, and therefore invalid, in light of a prior patent application by NuvaRing’s inventor for another vaginal contraceptive ring.