Shares of Amarin (AMRN -1.23%) were down 68% at 7:27 p.m. EDT in after hours trading, after a judge in the U.S. District Court of Nevada ruled for generic-drug makers Hikma Pharmaceuticals (HKMP.Y -1.34%) and Dr. Reddy's Laboratories (RDY -0.69%) in a lawsuit with Amarin over patents on Amarin's fish oil drug, Vascepa, which is approved to treat patients with inflated triglyercide levels.

Hikma and Dr. Reddy's filed abbreviated new drug applications (ANDAs) with the Food and Drug Administration to sell generic versions of Amarin's Vascepa, which prompted a lawsuit from Amarin claiming that the generics infringed on the company's patents.

Following a trial in January, the judge ruled today that the "defendants' proposed ANDA products will induce infringement of the asserted claims, but all the asserted claims are invalid as obvious."

One of the requirements for a patent claim is that the use isn't so obvious that it would be easy to realize that the invention could be used for the proposed use. Hikma and Dr. Reddy's obvious argument was based on the fact that GlaxoSmithKline's (GSK -1.04%) Lovaza, another fish oil product, was already approved as a treatment for high triglyceride levels.

Courthouse building

Image source: Getty Images.

Amarin's Vascepa sales increased 87% to $430 million in 2019 after Amarin showed that the drug improved cardiovascular outcomes in patients with moderately high triglyceride levels. The drug has been on the market since 2012 for patients with extremely high triglyceride levels, but the new data increased the potential market substantially.

Neither Hikma nor Dr. Reddy's has gained FDA approval for their generic drugs, and Amarin said it plans to seek a preliminary injunction to block the launch of a generic while the biotech files an appeal to the judges' decision.