Individuals taking extended-release injection naltrexone for opioid use disorder may be less likely to drop out of treatment after a single use of opioids compared with patients receiving placebo, according to study results published in Addiction.

This post-hoc analysis of a randomized placebo-controlled trial examining the effectiveness of extended-release injection naltrexone vs placebo for the treatment of opioid use disorder included data from 250 patients (average age, 29 years) who had completed inpatient detoxification within the previous 30 days.

Participants were randomly assigned to receive injections of extended-release naltrexone (n=126) or placebo (n=124) before discharge and then every 4 weeks for 24 weeks. Baseline characteristics were similar in both groups, with the exception of methadone use within 30 days of baseline (placebo, 14.6%; naltrexone, 8.7%), and the use of prescription opioids (naltrexone, 16.8%; placebo, 9.8%).

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The study’s primary outcome was time to treatment dropout, which was measured based on survival analysis and weekly urine drug tests for opioids, which were used as a time-dependent covariate.

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A significant interaction of time-dependent toxicology by treatment was established (P =.024). The risk for a urine drug test positive for opioids was found to increase the risk for treatment dropout the following week in patients receiving placebo (hazard ratio [HR], 6.25; 95% CI, 3.6-10.0), but not in participants receiving naltrexone (HR, 1.67; 95% CI, 0.6-4.5).

In addition, a greater percentage of patients receiving naltrexone vs placebo completed all 24 weeks of treatment without positive urine drug test results (31% vs 20%, respectively; P =.051).

Study limitations include the fact that dropout from treatment was used as a way to assess relapse.

 “These data support the model that [extended-release injection naltrexone], by blocking the reinforcing effects of opioids, leads to extinction of opioid-taking behavior, or blocks cue or priming effects of doses of opioids,” noted the study authors.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

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Nunes EV, Bisaga A, et al. Opioid use and dropout from extended-release naltrexone in a controlled trial: Implications for mechanism [published online July 17, 2019]. Addiction. doi:10.1111/add.14735