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.