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Background and Objectives

We tested long-acting injectable depot naltrexone for its tolerability, pharmacokinetics, and safety in Phase I.

Methods

The Phase I trial enrolled 36 healthy participants in two panels (A, B). In Panel A, 24 subjects were randomly assigned to the high-dosage group (400 mg naltrexone, n = 6; placebo, n = 6) or low-dosage group (200 mg naltrexone, n = 6; placebo, n = 6). In Panel B, 12 subjects were randomized to take six doses of monthly injectable naltrexone (400 mg) or placebo.

Results

After a single injection of naltrexone 200 and 400 mg, means (SD) of naltrexone plasma concentrations were .57 (.28) ng/ml and 1.5 (.8) ng/ml 30 days post-injection. There was no effect of accumulation after multiple dosing. Eleven of 30 subjects (36.67%) who were administered injectable depot naltrexone reported a total of 12 adverse events (AEs). Seven of these 11 AEs were coded as possibly related with study medication. All treatment-related AEs were mild in severity. No serious treatment-related AEs occurred.

Discussion and Conclusions

This long-acting formulation of injectable depot naltrexone is well tolerated, results in constant plasma concentration of naltrexone for at least 1 month.

Scientific Significance

The tolerability and safety of long-acting injectable depot naltrexone are good. (Am J Addict 2014;23:162–169)