(Corrects to add Mylan to list of defendants, paragraph 2; Removes incorrect reference to Teva as a unit of Mylan, paragraph 10)

By Brendan Pierson

Feb 1 (Reuters) - A federal appeals court ruled Monday that four patents related to Purdue Pharma's painkiller OxyContin are invalid, potentially bringing Teva Pharmaceutical Industries Ltd and others a step closer to introducing generic versions of the drug.

Privately owned, Connecticut-based Purdue had sued Teva, Amneal Pharmaceuticals, Epic Pharma and a U.S. arm of Mylan NV after they sought approval from the U.S. Food and Drug Administration to make generic OxyContin.

Monday's ruling by the Federal U.S. Circuit Court of Appeals upheld earlier orders from a lower court judge in favor of the generic drugmakers.

Purdue said in a statement that it was reviewing the decision and considering what to do next.

"Despite the court's ruling, Purdue has several other patents protecting OxyContin, and we do not anticipate generic manufacturers selling the product in the near future," it said.

Representatives of the generic drugmakers could not immediately be reached for comment.

Currently, the only generic versions of OxyContin on the market are so-called "authorized generics," which are exact copies of the brand-name version authorized by Purdue.

Three of the patents Purdue sought to enforce in its lawsuits are related to an improved formulation of oxycodone, the active ingredient in OxyContin.

The other patent describes technology designed to prevent abuse of the drug by making it difficult to crush and causing it to form a gel when dissolved in water so that it cannot be injected. Purdue licensed that technology from German pharmaceutical firm Grunenthal GmbH, which is also a plaintiff in the lawsuit.

Purdue's lawsuit against Teva went to a non-jury trial before U.S. District Judge Sidney Stein in Manhattan in 2013. In January 2014, Stein said that the patents were invalid because they did not add enough to what was already known.

Stein subsequently dismissed the lawsuits against Mylan, Amneal and Epic as well, since they were based on the same patents. Purdue appealed all four cases to the Federal Circuit.

The case is Grunenthal GmbH et al v Teva Pharmaceuticals USA Inc, U.S. Court of Appeals, Federal Circuit, No. 2014-1311.

(Reporting by Brendan Pierson in New York; Editing by Lisa Shumaker)