Drugmakers have long argued they should have the right to talk to doctors about unapproved uses for their products, as long as they are being truthful. And in some cases, courts have agreed.

But the federal government still frowns on the practice and, in recent years, has fined drug companies billions of dollars for talking to doctors about off-label uses for their medications.

On Thursday, Dublin-based Amarin Pharma took the unusual step of suing the Food and Drug Administration (FDA), arguing that it has a constitutional right to share certain information about its product with doctors, even though the agency did not permit the company to do so.

Lawyers for the company said they believed their case was the first time a manufacturer had pre-emptively sued the agency over the free-speech issue, before it had been accused of any wrongdoing. Other companies have sued the agency only after they have gotten into trouble.

"If you tell the truth – if you're not misleading – then the First Amendment protects you when you provide this sort of information," said Floyd Abrams, a noted First Amendment lawyer who is representing Amarin in the case, which was filed in US District Court in New York.

But others said that doing so sidesteps the authority of the FDA, which is responsible for making sure that drugs are safe and effective. "The First Amendment right is not an absolute right. It has limits. And it's always been subject to a balancing test," said Dr. Michael Carome, director of the health research group at Public Citizen, an advocacy group in Washington. "If this lawsuit were to succeed, it would be devastating for drug safety and undermine the drug approval process."

At issue in the lawsuit is the FDA's stance on Amarin's only product, Vascepa, which is a prescription Omega-3 fatty acid that is derived from fish.

In 2012, the FDA approved Vascepa for use in patients with extremely high levels of triglycerides, a kind of fat in the blood that has been linked to heart disease.

But when the company sought to expand the drug’s reach to a wider population of people with lower but still severe triglyceride levels, the agency turned it down. The company has said the FDA denied its request because, although a clinical trial showed the drug reduced triglycerides, it had not been proved to reduce the risk of heart disease.

Lawyers for Amarin say the company is not proposing to market Vascepa to a wider population of patients, merely to share with doctors the results of a 2011 company-sponsored clinical trial that showed the drug lowered triglycerides in patients with “persistently high” levels. It also wants to make statements about its product that it says match what manufacturers of fish-oil supplements – which are not regulated as stringently – are permitted to say: that “supportive but not conclusive research” shows Vascepa may reduce the risk of coronary heart disease.

Joel Kurtzberg, another lawyer for Amarin, said the company knew that doctors, who are permitted to prescribe off-label, were giving Vascepa to a wider pool of patients.

“It’s legal, it is done, it is commonplace,” he said. “Those doctors who are already prescribing off-label need more information, not less, about what their treatment options are.”

A spokeswoman for the FDA, Sandy Walsh, said the agency does not comment on pending litigation. – Copyright New York Times 2015