Serum naltrexone and 6-beta naltrexol concentrations in detoxified addicts during long term naltrexone treatment

The pourpose of the present study was to evaluate naltrexone and 6-b-naltrexol plasma time course during long term treatment in the usual clinical setting, in drug addicts. The plasma levels of naltrexone and 6-b-naltrexol were determined for 24 hours following an oral dose of 100 mg at the beginning and after months of naltrexone treatment. Our results showed large differences among patients in serum naltrexone and 6b-naltrexol levels. On the other hand, there were no differences in serum time course of both substances in the same patient over 3 months. Peak levels and AUCs of naltrexone were lower than those of 6b-naltrexol in 10 addicts and higher than those of the metabolite in 3 patients. No significant differences in the apparent half-lives of the two drugs were detected among groups. These data are consistent with the occurrence of a decreased first-pass metabolism of naltrexone in 3 patients leading to a larger availability of an oral dose.