Naltrexone implants -- duration, tolerability and clinical usefulness. A pilot study.

Naltrexone blocks opioid effects effectively, but poor compliance limits the clinical usefulness in the treatment of opioid dependence. Long-acting implanted formulations might increase the clinical feasibility. Several implants have been produced, but few clinical reports have been published. This paper describes an open trial with an Australian implant. This implant is claimed to have duration of up to six months with double implants and acceptable levels of side effects. This was explored in the present pilot study with 13 opioid-dependent patients. By single implant of 1.8 g naltrexone the duration judged by naltrexone plasma levels above 1 ng/ml naltrexone was between 2 and 4 months. Double implants maintained such plasma levels for 5-6.5 months. Clinically, the implants appeared promising. Side effects were minimal. During the period with adequate plasma levels of naltrexone, use of opioids was absent and use of other psychoactive drugs reduced. At 1-year follow-up, the patients rated the implants highly positively.