An advisory committee to the U.S. Food and Drug Administration has decided to back a new type of cholesterol-lowering drug made by Sanofi SA and Regeneron Pharmaceuticals, albeit with a few restrictions.

In a vote of 13-3, the panel approved the drug, Praluent, the first of its class of cholesterol-lowering drugs that effect cholesterol counts by inhibiting a protein known as PCSK9.

However, most of the panelists said they would like to see limits placed on the new drug, at least initially. Instead of making it widely available, the panel recommends using it for patients with a genetic predisposition to high cholesterol and those that are at a high risk of cardiovascular disease, who are already taking the maximum doses of statin therapy, the traditional cholesterol lowering therapies that are available.

Panelists prefer to see the results of a large ongoing trial, assessing whether the drug's LDL lowering effects translate into reduced cardiovascular risk before recommending it to a wider population of patients.

Typically, the FDA follows the recommendations of the advisory panel, but it is under no obligation to do so. A second drug, Amgen Inc's Repatha, is also being considered by the panel. If the drugs are approved, they are expected to generate annual sales of more than $2.5 billion each by 2020.

The panel did express some concerns about suggestions in the data that the drug could increase the risk of diabetes, but said currently it is unclear how meaningful the risk actually is. There were also concerns that the drug may impact cognition and the liver. The panelists conceded that the drug may have to be used on millions of patients before such risks can be properly assessed.

They also expressed concern that the drug could lower LDL too much when taken in combination with a statin and believe that physicians could try to compensate by taking patients off statins or reducing their dosage. That concern was previously expressed by the FDA in its previous briefing documents.

Praluent is designed to be given every other week by injection, while Amgen's drug would given every other week, or once a month in a larger dose.

Statins were originally developed in the 1980s. This development of this latest line of cholesterol reducing drugs marks the first major advancement in cholesterol reduction in decades and could provide an effective solution for patients that simply cannot tolerate the side effects of statins.