A cheaper version of Johnson & Johnson’s top-selling drug, the rheumatoid arthritis treatment Remicade, could be available in the U.S. two years early after a federal judge ruled a key patent on the drug invalid.

J&J, based in New Brunswick, New Jersey, said Wednesday it plans to appeal the ruling.

The appeal process could take a year or more. In the meantime, rival drugmaker Pfizer plans to begin selling its nearly identical version of Remicade, called Inflectra. This so-called “biosimilar” drug was approved by the Food and Drug Administration in early April. Pfizer can legally begin selling Inflectra Oct. 3, though J&J will attempt to block Pfizer’s launch through its appeal.

The patent that was ruled invalid would have covered the drug until September 2018.