A US federal appeals court has rejected an appeal by Danish biopharma Forward Pharma against the validity of Biogen’s patent for blockbuster multiple sclerosis (MS) drug Tecfidera.

The ruling frees Biogen from having to pay future royalty payments to Forward Pharma for the drug and secures the US biotech’s exclusivity on Tecfidera until 2028. Tecfidera had sales of around $4.2 billion in 2017.

The court said it agreed with a March 2017 ruling by the Patent Trial and Appeal Board (PTAB) that validated Biogen’s patent. The two companies have been locked in a dispute relating to the dosage (480 mg) of the drug’s key ingredient dimethyl fumarate (DMF).

Biogen had previously agreed in January 2017 to pay Forward Pharma $1.25 million to license the Danish group’s intellectual property if the PTAB were to rule against the US biotech. The agreement would have allowed Forward Pharma to receive additional royalty payments if it had won the Federal Circuit appeal.

Claus Svendsen, Forward Pharma’s CEO, said it was disappointed with the court’s decision and the company was considering its options and response.

Forward Pharma is also appealing against the European Patent Office’s decision in January 2018 to revoke its patent on a PH-controlled release pharmaceutical composition containing DMF.