A U.S. appeals court affirmed a win on Monday for Swiss drugmaker Novartis Pharmaceuticals Corp against Chinese generic drugmaker HEC Pharm Co Ltd, finding that a patent covering the blockbuster multiple-sclerosis drug Gilenya is valid and a proposed HEC generic would infringe it.

A divided panel of the U.S. Court of Appeals for the Federal Circuit rejected HEC's argument that the patent lacked a proper written description, thwarting the company's bid to sell a generic version of Gilenya before the patent expires.

Novartis sued HEC in Delaware federal court after HEC applied for U.S. Food and Drug Administration approval of the generic. Novartis settled with several other generic drugmakers that had also been involved in the litigation, allowing for some Gilenya generics before the patent's 2027 expiration.

According to a company report, Novartis made more than $3 billion from Gilenya sales last year, making it the company's second-highest selling drug.

After a 2020 bench trial, then-U.S. District Judge Kent Jordan affirmed the validity of Gilenya's patent, which covers a method of treating relapsing multiple sclerosis with a specific dose of the drug fingolimod, and found HEC's proposed generic infringed.

A 2-1 Federal Circuit panel rejected HEC's argument on appeal that the patent was invalid because it failed to properly describe the dosage.

U.S. Circuit Judge Kathleen O'Malley wrote the majority opinion, joined by Circuit Judge Richard Linn.

In a dissent, Chief Circuit Judge Kimberly Moore took issue with upholding a limitation on the dosage that she said wasn't supported by the patent's written description.

The case is Novartis Pharmaceuticals Corp v. HEC Pharm Co Ltd, U.S. Court of Appeals for the Federal Circuit, No. 21-1070.