Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

ReVia (Orphan Australia)
50 mg tablets
Approved indication: substance abuse
Australian Medicines Handbook Section 18.5

Naltrexone is an opioid antagonist. It can be used in the management of patients who have ceased using opioids and as part of a treatment program for alcohol dependence. While naltrexone blocks the effects of opioids, e.g. injected heroin, its mechanism of action in alcohol-dependent patients is unknown. In animals, opioid antagonists reduce alcohol consumption.

The main steps in the treatment of opioid addiction are detoxification and maintenance of abstinence. Although naltrexone has been used in rapid detoxification regimens, the evidence is not strong enough for this technique to be considered to be more than experimental.1 Naltrexone's main use will therefore be in maintenance. By blocking opioid receptors, naltrexone stops the euphoric effects of heroin which may reduce the patient's desire for the illicit drug.

A Cochrane review is investigating the effectiveness of naltrexone maintenance as there are no data which clearly show a beneficial effect on the rate of relapse. Patients must be motivated to comply with one of a variety of treatment regimens, so it is best if the drug is part of a comprehensive rehabilitation program.

Great care is needed when starting treatment. The patient should not have taken any opioids in the preceding 7-10 days. If they have, there is a risk of precipitating an acute withdrawal reaction. The product information recommends a naloxone challenge test if there is any doubt about the patient's abstinence.

Patients need to be warned not to try to overcome the blockade by taking large quantities of opioid; they may overdose. They should also be aware that their sensitivity to opioids may increase, so if they relapse after treatment, their `usual' dose may cause life-threatening adverse effects.

In the treatment of alcohol dependence, 50 mg naltrexone is taken daily for up to 12 weeks. In clinical trials, this regimen has produced better abstinence rates than placebo and reduced the risk of relapse. As with opioid maintenance treatment, patients must be motivated so naltrexone should only be used as one part of a treatment program. Patients who drink heavily may have abnormal liver function. If liver function tests are more than 3 times normal, it may be inappropriate to use naltrexone as the drug can damage the liver.

First-pass metabolism reduces the oral bioavailability of naltrexone to 40%. Extensive metabolism results in only 2% being excreted unchanged with most of the metabolites appearing in the urine.

Commonly reported adverse events include nausea, headache, fatigue, insomnia and anxiety. Although depression and suicidal ideation have been reported, no causal link with naltrexone has been shown.