The U.S. Court of Appeals for the Federal Circuit has denied Biogen’s request to revive a patent dispute involving its blockbuster multiple sclerosis drug Tecfidera (dimethyl fumarate).

Biogen has accused Viatris, formerly Mylan Pharmaceuticals, of infringing on a key patent of the drug.

In November 2021, the federal appeals court affirmed a June 2020 decision by the U.S. District Court for the Northern District of West Virginia, which deemed the patent invalid because it didn’t adequately describe how Tecfidera treated multiple sclerosis.

At this point, Biogen’s only avenue to block Viatris from marketing a generic version of Tecfidera is for the Supreme Court to take up the case.

Tecfidera sales topped $1.9 billion globally in 2021.