A U.S. appeals court on Tuesday ruled that a patent related to Swiss drugmaker Novartis AG’s blockbuster multiple sclerosis drug Gilenya was invalid, potentially paving the way for introduction of a cheaper generic version of the medicine.

The U.S. Court of Appeals for the Federal Circuit, which hears patent appeals, reversed its own earlier ruling in the case. The finding by a divided panel revives Chinese drugmaker HEC Pharm Co’s bid to make a generic version of the drug.

Novartis reported nearly $2.8 billion in Gilenya sales last year, making it the Swiss company’s third-highest-selling drug. The company said in a statement that it is considering “all available options” to defend the patent and plans to ask the full Federal Circuit to review the decision, which may take several months.

Novartis also said it believes HEC and others cannot launch generic versions of Gilenya during the ongoing appeal process. HEC and its attorneys did not immediately respond to requests for comment on the decision.

The Federal Circuit in January upheld a Delaware court’s ruling that Novartis’ patent was valid and that HEC’s proposed generic infringed it. The patent covers use of a specific dosage of Gilenya, known chemically as fingolimod, to treat relapsing multiple sclerosis.

A split panel with two of the same judges reversed the decision on Tuesday.

Novartis has settled patent cases with several other generic drugmakers, paving the way for some Gilenya generics to be introduced before the patent’s 2027 expiration.

Novartis said after the January decision that it did not expect any Gilenya generics on the U.S. market for at least the next two years.