Shares of Hyderabad-based Natco Pharma fell to a five-month low after the U.S. Supreme Court decided to hear an appeal by Teva Pharmaceutical Industries which seeks to delay the introduction of generic versions of Teva's blockbuster multiple sclerosis drug, Copaxone.
The patent which was originally set to expire in May 2014 would be delayed to September 2015, if the Israel-based company wins the appeal.
The drug, which accounts for more than half of Teva's profit, grossed $3.2 billion in annual sales in the United States for Teva.
"The company continues to believe that Teva's '808 patent is invalid for indefiniteness," Natco said in a statement.
Novartis' generic drug focused subsidiary Sandoz along with Momenta Pharmaceuticals and Mylan are the other companies involved in the litigation.
Natco shares were trading down 16% at Rs 671.95 on noon on Tuesday on the BSE Sensex.