Teva Pharmaceutical Industries, U.S. subsidiary of the Israeli generics drugmaker, has asked the U.S. Supreme Court to stop a lower court ruling from going into effect while the justices consider an appeal in a patent fight over Teva's top-selling multiple sclerosis drug Copaxone.

On March 31, the high court agreed to hear Teva's appeal of a July 2013 ruling by a U.S. court of appeals that favoured two teams developing cheaper generic forms of Copaxone. One of the teams involved Novartis subsidiary Sandoz with Momenta Pharmaceuticals, the other Mylan with Natco Pharma.

The appeals court had upheld some of the nine patents related to the drug, or portions of them, but declared several invalid, so that patent protections were set to expire in May 2014 instead of September 2015.

The company's lawyers said in the court filing that if the appeals court ruling was not stayed, "Teva's innovative and widely prescribed treatment for multiple sclerosis will lose protection."

The Supreme Court will not hear oral arguments in the case until its 2014 term begins in October, with a ruling not widely expected before June 2015. If the court does not act on the stay application, the ruling could come "effectively too late to prevent irreparable harm to Teva," the lawyers said.

The drugmaker is currently trying to switch patients to a new version of Copaxone, its most important product.