Antagonist Models for Relapse Prevention and Reducing HIV Risk.

Abstract

Naltrexone is an antagonist that binds tightly to μ-opioid receptors and blocks the subjective and analgesic effects of opioids. It does not produce physiologic dependence and precipitates withdrawal if administered to an opioid dependent person, thus starting it must begin with detoxification. It was first available in the mid-1970s as a 50mg tablet that blocked opioids for 24-36h if taken daily, or every 2-3days at higher doses - for example: 100mg Monday and Wednesday, 150mg on Friday. From a pharmacological perspective it worked very well and was hoped to be an effective treatment but results were disappointing due to low patient interest and high dropout followed by relapse. Interest in it waned but rose again in the late 1990's when injecting opioid use and the rapid spread of HIV in the Russian Federation converged with an international interest in reducing the spread of HIV. One result was a series of meetings sponsored by the U.S. National Institute on Drug Abuse (NIDA) and Pavlov State Medical University in St. Petersburg, Russian Federation, on ways to reduce the spread of HIV in that country. Addiction treatment was a clear priority and discussions showed that naltrexone could have a role since agonist treatment is against Russian law but naltrexone is approved and the government funds over 25,000 beds for detoxification, which is the first step in starting naltrexone treatment. These meetings were followed by NIDA studies that showed better compliance to oral naltrexone than in prior U.S. studies with the expected reductions in HIV injecting risk for those that stayed in treatment. These events and findings provided a background and identified an infrastructure for the study that led to FDA approval of extended release injectable naltrexone for preventing relapse to opioid dependence. This paper will briefly review findings from these studies and end with comments on the potential role of extended release naltrexone as a meaningful addition to current pharmacotherapies for treating opiod dependence and reducing HIV risk.