The U.S. Food and Drug Administration has delayed action on Amarin Corp. plc’s supplementary New Drug Application for heart pill Vascepa and will consider reinstating an agreement that the agency earlier had unilaterally dropped.

The FDA moves gave hope to investors who have suffered an 80 percent decline in the company’s share price over the past two months. In early trading on the Nasdaq exchange today, Amarin’s share price rose 47 cents - about 30 percent - in a little over two hours.

Amarin, an Irish biotech firm with research headquarters in Groton, made the announcement today and said it had been notified of the FDA’s move late Thursday. The FDA had been expected to take final action today on Amarin’s request for re-labeling Vascepa as a combined therapy with statins, and analysts had expected the agency to deny the application based on a panel’s 9-2 vote against approval.

But now the FDA, according to an Amarin regulatory filing, will reconsider its earlier decision to unilaterally drop a Special Protocol Assessment agreement that had seemed to doom chances for Vascepa to quickly tap into a much wider pool of heart patients than the company can reach with its current labeling.

“Amarin plans to continue to work with the FDA to pursue reinstatement of the ... agreement and approval of the (supplementary indication),” the company said in a press release today. “There can be no assurance that Amarin will be successful in this effort.”

Vascepa is currently approved only for patients with unusually high levels of triglycerides, a form of fat, in their blood. The new labeling would target a larger pool of patients on statin therapy with elevated but not extremely high triglyceride levels.

The FDA said it would decide by Jan. 15 whether to reinstate the special protocol agreement, which backed Amarin’s drug-study design methods.

The FDA panel that recommended against expanded labeling for Vascepa had questioned study results that showed improvements in patient triglyceride profiles but failed to demonstrate that the medicine reduced the incidence of heart attack. Had the FDA rubber-stamped the panel’s recommendations, Amarin would have been forced to complete about two years of further studies before Vascepa would have been considered again for add-on statin therapy.

No date was given for the FDA to decide on the supplementary application.