Naltrexone treatment for opioid dependence: does its effectiveness depend on testing the blockade?

Area of Science:

• Neuroscience
• Pharmacology
• Addiction Medicine

Background:

• FDA-approved injectable naltrexone (Vivitrol) for opioid dependence necessitates understanding antagonist treatment mechanisms.
• Learning principles suggest antagonists extinguish drug-seeking behavior by blocking reinforcement from drug use.
• Hypothesis: Opiate use moderates naltrexone's effect, with positive urines preceding dropout in placebo but not active-medication groups.

Purpose of the Study:

• To evaluate the efficacy of low (192 mg) and high (384 mg) doses of long-acting injectable naltrexone (Depotrex) compared to placebo.
• To determine if opiate use moderates treatment outcomes in patients undergoing naltrexone therapy.

Main Methods:

• An 8-week, double-blind, placebo-controlled trial involving 57 participants.
• Cox proportional hazard model used to analyze time-to-dropout based on treatment assignment and urine toxicology.
• Comparison of low-dose naltrexone, high-dose naltrexone, and placebo groups.

Main Results:

• Significant interaction between opiate urines and treatment group.
• Opiate-positive urines predicted dropout in placebo and low-dose groups, but less so in the high-dose group, where abstinence was more likely.
• Higher retention rates were observed in both naltrexone groups compared to placebo when patients had no opiate-positive urines.

Conclusions:

• Injectable naltrexone facilitates extinction of drug-seeking behavior following opiate use.
• Adequate dosage is crucial; low-dose naltrexone showed similar dropout rates to placebo after opiate-positive urines.
• Naltrexone may have direct effects on opiate-taking behavior beyond extinction, potentially by reducing craving or normalizing neurobiological systems.