The U.S. Supreme Court refused to hear appeals brought by Purdue Pharma LP for a patent infringement case centered on reformulations of the painkiller OxyContin, clearing several barriers to the development of generics.

The high court denied a petition from the branded drugmakers to overturn a lower court ruling that invalidated four patents covering OxyContin formulations containing reduced levels of 14-hydroxy and abuse-deterrent properties. No explanation accompanied the court’s denial.

The refusal lets stand U.S. Court of Appeals for the Federal Circuit rulings that nixed the patents on the grounds of obviousness and prior reference stand. The companies petitioned the high court after losing the case on appeal to a three-judge panel for the Federal Circuit and requesting a rehearing before the full appeals court.