Adherence monitoring in naltrexone pharmacotherapy trials: a systematic review.

OBJECTIVE: The efficacy of naltrexone (Revia, Vivitrol) for the treatment of alcohol dependence exhibits a high degree of heterogeneity. The aim of the current study was to evaluate the extent to which variability in patient adherence to treatment contributed to the range of clinical responses observed during naltrexone treatment.
METHOD: A systematic review was conducted of efficacy trials of naltrexone for the treatment of alcohol dependence to evaluate the level of adherence monitoring.
RESULTS: Of 49 identified trials, 22 (49%) met the inclusion criteria of being randomized, double-blind, placebo-controlled trials that reported adherence. The "adherence-assurance score" of these trials was calculated as a function of the frequency with which "low," "moderate," or "high" confidence levels of adherence monitoring were used. Of these 22 randomized, controlled trials, only 3 (14%) met criteria for high levels of adherence assurance, 5 (23%) met medium adherenceassurance criteria, and 14 (64%) met low adherence criteria. Of the three high-assurance studies, one used direct supervision of thrice-weekly oral dosing of naltrexone, and two used extended-release injectable formulations of naltrexone administered once per month. The Spearman correlation between risk ratios for return to heavy drinking (for naltrexone vs. placebo) and the level of adherence assurance (low vs. medium vs. high) was significant (r = -.62, p = .025).
CONCLUSIONS: These findings suggest that the modest effect sizes for naltrexone reported in systematic reviews and meta-analyses may be attributable, at least in part, to variability in naltrexone adherence rates. High-assurance adherence strategies should be standard practice in clinical trials of medications being evaluated for the treatment of alcohol dependence.