(Reuters) – Shares of Amarin Corp plunged nearly 70% on Tuesday after the drugmaker lost a major U.S. patent battle for its heart drug Vascepa, opening the door for generic competition to its main revenue contributor.

Amarin claimed in a patent lawsuit that generic versions of Vascepa produced by drugmakers Hikma Pharmaceuticals Plc and Dr. Reddy’s Laboratories infringed on six of its U.S. patents.

But the Nevada District Court ruled late Monday that the claims on the fish-oil derivative Vascepa were “obvious”, and therefore invalid.

The U.S. Food and Drugs Administration has not yet approved any generic version of Vascepa. If it does, Amarin will seek to prevent the launch of generic versions of the drug by filing a preliminary injunction, the company said.

But that will not protect it from generic rivals closing in, Oppenheimer analyst Leland Gershell said.

“We put generic launches in 2022-23 as a best case for Amarin, yet despite a presumed injunction, at-risk launches could occur much sooner,” Gershell said.

Amarin’s Vascepa was first approved in 2012 to lower high triglycerides and recently won approval for expanded heart benefit claims that lets it tap into a market of up to 15 million Americans.

The coronavirus outbreak has also impacted the company’s recent sales efforts as Amarin earlier this month suspended in-person interactions of its sales representatives.

Amarin shares were down 69.9% at $4.10 before the bell.

(Reporting By Mrinalika Roy in Bengaluru; Editing by Saumyadeb Chakrabarty)