Naltrexone is an opioid antagonist indicative as option for adjunctive prophylactic therapy for maintenance of detoxified, formerly opioid-dependent patients
- competitively displaces opioid agonists (for example, diamorphine or methadone), blocking the euphoric and other effects of opioids and thereby minimising the positive rewards associated with their us
NICE state, with respect to use of naltrexone in the management of opioid dependence (1):
- recommended as a treatment option in detoxified formerly opioid-dependent people who are highly motivated to remain in an abstinence programme
- should only be administered under adequate supervision to people who have been fully informed of the potential adverse effects of treatment
- should be given as part of a programme of supportive care
- effectiveness of naltrexone in preventing opioid misuse in people being treated should be reviewed regularly. Discontinuation of naltrexone treatment should be considered if there is evidence of such misuse
- the 'Summary of product characteristics' (SPC) states that naltrexone is licensed for use as an adjunctive prophylactic treatment for detoxified formerly opioid-dependent people (who have remained opioid free for at least 7-10 days) - note that there are long-lasting formulations of naltrexone in development (depot preparations and implants)
- naltrexone is rapidly absorbed, metabolised by the liver and excreted in the urine with an elimination half-life of 4 hours. Liver function tests are recommended before and during naltrexone treatment to check for liver impairment
- naltrexone is associated with opioid withdrawal symptoms if people are opioid dependent
- the SPC recommends challenge testing with naloxone hydrochloride (a shorter-acting injectable opioid antagonist) to screen for the presence of opioids if it is not certain whether the person is detoxified
- pople may be at risk of a fatal overdose caused by respiratory depression if they relapse while taking naltrexone. This can happen if the person tries a larger dose of diamorphine to achieve euphoria, or if they return to diamorphine use after naltrexone treatment, because of loss of tolerance to diamorphine
- suggested dosing:
- 25 mg naltrexone on day 1 followed by 50 mg daily thereafter for an initial period of 3 months
- extended treatment may be necessary because time to full recovery from opioid dependence is variable
- three-times-a-week dosing schedule may be considered if it is thought likely to improve compliance with treatment
A systematic review states that Naltrexone appears to have some limited benefit in helping formerly opioid-dependent individuals to remain abstinent, although the quality of the evidence is relatively poor and heterogeneous (2).
Naltrexone implants for opioid abuse:
- a study by Comer et al found a dose-dependent relationship, such that larger doses of sustained-release naltrexone were associated with lengthened treatment and less self-reported need for heroin (3)
- a further study using naltrexone implants found that patients receiving naltrexone had on average 45 days less heroin use and 60 days less opioid use than controls in the 180-day period (both P<0.05)
- the study authors concluded that naltrexone implant treatment safely and significantly reduces opioid use in a motivated population of patients (4)
- a systematic review (Lobmaier et al., 2008) investigated non-RCT studies of sustained-release naltrexone to assess adverse effects, and preliminary evidence suggests that adverse effects to sustained-release previous naltrexone were not different from oral naltrexone, though higher rates of adverse effects occur on naltrexone compared to placebo (5)
The summary of product characteristics should be consulted before prescribing this drug.
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