GAITHERSBURG, Md. » Federal health advisers on Tuesday recommended approval for a highly anticipated cholesterol drug from Sanofi and Regeneron Pharmaceuticals, but with the caveat that more data is needed about its long-term ability to reduce heart attacks.

The expert panel recommended by a 13-3 vote that the Food and Drug Administration approve the injectable drug, called Praluent.

But in an unexpected development, a number of panelists said the drug should only be used in patients with abnormally high cholesterol levels caused by an inherited disorder. Those panelists said they wanted to see more data about whether the drug ultimately reduces heart problems, before it is used more broadly.

"I personally fall on the side of having optimism, but I need to see the cardiovascular outcome study to know," said Dr. Philip Sanger of Stanford University, who voted for the drug.

If the FDA follows the group’s recommendation, the drug could be approved for a much smaller population than its developers have proposed.

Praluent is part of a new class of injectable drugs that lower cholesterol more than older medications called statins, which have been the standard treatment for more than 20 years. A similar drug from Amgen will go before the same panel on Wednesday.

Both drugs block a substance called PCSK9, which interferes with the liver’s ability to remove cholesterol from the blood. Analysts expect the drugs to grow into blockbuster sellers, generating billions of dollars in new sales. But Tuesday’s meeting underscores the uncertainty about who should receive such medications.

More than 73 million U.S. adults, or nearly one-third, have high LDL cholesterol, according to the Centers for Disease Control and Prevention. Those patients have twice the risk of heart disease, the leading cause of death in the U.S.

Paris-based Sanofi and Regeneron, which is based in Tarrytown, New York, have suggested marketing their drug to a large group of patients, including those who are at high-risk for heart attacks and those who cannot tolerate statin drugs due to side effects.

But many panelists said they would limit the drug’s use to a much narrower group of patients who have abnormally high cholesterol levels caused by a family disorder.

"I am really only comfortable with the risk-benefit equation in that population," said Michele Orzsa, the panel’s consumer representative.

Key to the panel’s decision was whether lowering bad, or LDL, cholesterol translates into reduced heart attacks. For over 20 years, the FDA has used reduced LDL levels as a benchmark to approve cholesterol drugs, including statins like Lipitor and Zocor.

But recent studies of drugs like niacin have shown that reducing cholesterol levels does not always lead to reductions in heart attack, stroke and related problems.

The FDA’s internal scientists pressed panelists on whether they thought lower LDL cholesterol was still an accurate predictor of a drug’s benefit.

"I don’t believe we have enough data today to say that LDL, with a new drug class, is sufficient for approval," said Dr. William Hiatt, of the University of Colorado’s School of Medicine, who voted against the drug.

Despite the measured endorsement, company representatives said they were "gratified" by the meeting’s outcome.

"This is one of the next big milestones for this product and the promise it can deliver to patients," Bill Sasiela, a vice president with Regeneron Pharmaceuticals Inc.

Regeneron’s stock fell about 3 percent in extended trading following the announcement. Sanofi’s U.S.-traded shares rose about 1 percent.