Naltrexone. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic efficacy in the management of opioid dependence.

Naltrexone is a long acting competitive antagonist at opioid receptors which blocks the subjective and objective responses produced by intravenous opioid challenge. It is suitable for oral administration, and has been studied as an adjunct for use in opioid addiction management programmes. In non-comparative clinical trials involving detoxified patients, oral naltrexone reduced heroin craving and between 23 and 62% of patients remained in treatment after 3 to 4 weeks. However, in two studies 32 to 58% of patients who continued in treatment were opioid-free between 6 and 12 months after stopping naltrexone. As might be expected studies involving highly motivated patients have shown this type of patient group to achieve greater treatment success rates during naltrexone therapy, and remain opioid-free longer than other groups of apparently less motivated patients. In addition, when naltrexone is combined with family support, psychotherapy and counselling, patients are more likely to remain opioid-free. Naltrexone produces a low incidence of side effects, with gastrointestinal effects being the most commonly reported symptoms. Thus, despite the overall high attrition rates from trials, in selected patient groups and in combination with appropriate support mechanisms and psychotherapy, naltrexone represents a useful adjunct for the maintenance of abstinence in the detoxified opioid addict.