Shares in Irish pharmaceuticals group Amarin slumped more than 20 per cent yesterday as the US regulator shut the door on the company's plans to extend the market for its Vascepa purified Omega-3 fish oil drug in treating patients at risk from cardiovascular disease due to elevated blood fat levels.

In a statement, Amarin told the market the Food and Drug Administration’s Office of New Drugs had denied its appeal of the decision to withdraw approval of its Anchor clinical trial, designed to expand its market for the drug by including patients with lower but still elevated levels of blood fats.

Last October, the FDA raised doubts over whether fish oil drugs could improve cardiovascular outcomes. It also questioned the design of the trial.

Last night, Amarin said it was evaluating “potential next steps”.