Updated from 4:34 p.m. EDT

Alkermes

(ALKS) - Get Report

and

Cephalon

(CEPH)

said Thursday that they have received approval to market their new alcoholism treatment Vivitrol.

The drug has been touted by the companies as a way to improve patient compliance because it is a once-a-month injectable medication rather than a daily pill. Vivitrol is an extended-release formulation of an existing, now-generic alcoholism treatment pill called naltrexone. Vivitrol must be administered by a physician or other healthcare professional.

Vivitrol will be available by the end of June, said executives of both companies in a telephone conference with analysts on Thursday afternoon. They won't reveal the drug's price until just before Vivitrol is launched.

The drug is approved by the Food and Drug Administration for people who are able to abstain from drinking in an outpatient setting and who aren't drinking when they take the drug. Vivitrol "should be used in combination with psychosocial support, such as counseling or group therapy," the companies said.

Alkermes, which developed the formulation, and its marketing partner, Cephalon, announced the FDA's approval a few minutes before markets closed. In regular trading, Alkermes' stock closed up 89 cents, or 4.2%, at $21.96. After hours, the stock rose another 97 cents, or 4.4%. In regular trading, Cephalon gained 80 cents to $60.20. After hours, the stock added 32 cents.

According to an agreement signed last June, Cephalon has primary responsibility for marketing and sales while Alkermes will handle the manufacturing. Alkermes receives a milestone payment of $110 million from Cephalon thanks to the FDA's ruling.

Frank Baldino Jr., chairman and CEO of Cephalon, said his 120-member salesforce will initially contact a core group of physicians who treat alcoholism - some 2,000 to 3,000 addiction specialists. The company plans to approach the 2.2 million alcoholics in the U.S. who have sought treatment as well, then expand their efforts to other alcoholics and other physicians whose patients haven't sought treatment.

The companies say clinical trials show that most of Vivitrol's side effects "were mild to moderate in intensity." The most common side effects are nausea, vomiting, headache, dizziness, fatigue and injection site reactions.

However, Vivitrol's label carries a black box warning -- the toughest alert required by the FDA - about potential liver damage. The warning says that naltrexone can cause liver damage "when given in excessive doses," adding that doctors should be aware of the side effects if their patients have liver disease. The label says Vivitrol "does not appear to be

toxic to the liver at the recommended doses." Still, patients must be warned of liver damage risks.

The FDA

granted conditional approval for the drug in December, saying it needed some additional preclinical data and required further discussions with the companies about the drug's label. The companies had expected to hear from the FDA last September, but the agency said before the deadline that it needed another 90 days to study their application.