The Food and Drug Administration has approved a once-a-month injectable version of a medicine that helps alcoholics stop drinking, making it easier for them to stay in treatment.

Vivitrol, made by Cephalon Inc. and Alkermes Inc., is an extended-release suspension of naltrexone, a medicine that binds to the brain's natural opioid receptors. Blocking these receptors leads to reduction in alcohol-seeking behavior by helping control cravings, studies have shown.

"This is an important advance," said Dr. Herbert Kleber, professor of psychiatry and director of the substance abuse division at Columbia University.

"Naltrexone is the ideal drug, but we can't get patients to keep taking it. By improving compliance, they will benefit from its effects."

A once-a-month injectable also may reach more people, Kleber said. Only a fraction of the 18 million Americans dependent on alcohol are in a treatment program. Of those who do seek treatment -- about 2 million people -- more than 75 percent will return to drinking within a year, studies have found.

Vivitrol, which was approved by the FDA Thursday, April 13, 2006 and will be available by prescription beginning in June 2006, provides an alternative to oral medications that must be taken daily, freeing alcoholics from having to make a decision each day to take their medicine.

The pill versions are sold generically and under the brand name ReVia by Barr Pharmaceuticals Inc.

The injectable drug was developed by Alkermes, of Cambridge, Mass., which will manufacture Vivitrol, while Cephalon, of Frazer, Pa., will control marketing and sales.

Medicines alone won't do the trick, Kleber said: Therapy is also important.

The injectable is not going to be used to get people through the initial withdrawal symptoms when stopping alcohol. But once they are free of their cravings, it will help keep those cravings at bay, the companies said.