Kate Johnson

April 18, 2011

April 18, 2011 (Washington, DC) — Older age may reduce the likelihood of abstinence and treatment retention among opioid-dependent subjects treated with extended-release naltrexone (Vivitrol, Alkermes), according to research presented here at the American Society of Addiction Medicine 42ndAnnual Medical-Scientific Conference.

The findings are "a bit of a surprise because it's usually the other way round in addiction treatment," commented Edward Nunes, MD, from New York State Psychiatric Institute at Columbia University, New York City.

Dr. Nunes presented preliminary results from his secondary analysis of a Russian study, which showed efficacy of extended-release naltrexone over placebo for opioid dependence.

Extended-release naltrexone has been approved for the treatment of alcohol dependence since 2006 and was approved for the treatment and prevention of relapse in opioid dependence in October 2010 based on results from the Russian study.

In that randomized, double-blind, placebo-controlled trial, 126 patients were treated for 24 weeks with a once-monthly injection of extended-release naltrexone (380 mg) and 124 patient received an equivalent placebo injection.

The mean age of patients in both groups was 29.4 and 29.7 years, respectively, and all had undergone a mean of 18 days of inpatient detoxification before the trial.

At the end of the study, the treatment arm had significantly more weeks of abstinence, verified by urine tests, compared with the placebo group (90% vs 35%).

The high placebo response rate was a surprise in that study, said Dr. Nunes, "most of us would expect a higher relapse rate in a US population." But that finding offered some clues to possible predictors of response, he explained.

"A lot of the subjects were relatively young patients who lived with their families — so their families were imposing a fair amount of structure on them and that might be one of the reasons why the placebo response rate was surprisingly high."

This same reasoning may explain why youth (<30 years old) was identified as a predictor of good response, he said.

Among study subjects 30 years or older, the odd ratios for retention in the 6 months of treatment and abstinence at the end were 0.61 and 0.33, respectively, compared with younger subjects, he reported.

Among younger subjects, posttreatment abstinence was seen in 25.7% of the placebo group and 37.6% of the treated group, whereas in older subjects the rates were 12% and 17.1%, respectively.

Across all age groups, retention in the 6 months of treatment was just below 40% in the placebo group and just above 50% in the treatment group.

Asked to comment on the findings Gavin Bart, MD, chair of the meeting's Medical-Scientific Program Committee and assistant professor of medicine and director of the Division of Addiction Medicine at the University of Minnesota Medical School in Minneapolis, said he has concerns about depot naltrexone for the treatment of opiate dependence.

"We have medications for opioid dependence — methadone and buprenorphine — which are incredibly successful, with 1-year retention rates of approximately 70%. What we saw from the data today is that compared to placebo there was a 6-month retention of approximately 50% — so already at 6 months it's not as good as methadone and buprenorphine at 1 year.

"I think we need to do either a noninferiority study to show that depot naltrexone is as effective, and if it's not as effective, then we really need to make sure that methadone and buprenorphine become the standard of care and that depot naltrexone only be reserved for those who refuse these other medications or until we can identify a subset who may be most likely to respond," said Dr. Bart.

Dr. Nunes declared that that the study was funded by Alkermes. He also reports he receives research support from Alkermes and that his coauthors are all either current or former employees of the company. Dr. Bart has disclosed no relevant financial relationships.

American Society of Addiction Medicine (ASAM) 42nd Annual Medical-Scientific Conference: Abstract P4. Presented April 15, 2011.

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