Naltrexone

How it works

It competitively blocks opioid receptors, abolishing the euphoric and other effects of exogenous opioids and modulating alcohol-related reward pathways.

Prescribing in practice

• It can precipitate acute, severe opioid withdrawal in opioid-dependent patients, so the patient must be opioid-free for an adequate period (confirmed where appropriate) before starting.
• Because it blocks opioid analgesia, plan alternative pain management and warn that attempts to override the block with large opioid doses risk fatal overdose, especially after treatment stops when tolerance is lost.
• Assess liver function before and during treatment, as hepatotoxicity has been reported at higher doses.

Monitoring

Monitor liver function and adherence, and review ongoing abstinence and psychosocial support during treatment.

Counselling the patient

• Carry information that you are taking an opioid blocker so emergency teams can plan pain relief.
• Do not try to overcome the blockade with opioids, and remember your tolerance falls after stopping, raising overdose risk.

Evidence & guidelines

Naltrexone as part of a relapse-prevention programme is supported by NICE guidance on alcohol-use and opioid-dependence management.