A 32-year-old man with alcohol use disorder requests naltrexone. On detailed history he admits he used intravenous heroin three days ago and continues occasional opioid use. Why should naltrexone be avoided in him at present?
- A It will precipitate acute opioid withdrawal ✓
- B It causes severe hepatotoxicity when combined with opioids
- C It blocks the analgesic effect of alcohol
- D It reduces the efficacy of future opioid agonist therapy
Correct answer: A. It will precipitate acute opioid withdrawal
Explanation
Naltrexone is a competitive mu-opioid receptor antagonist. If any opioid remains on receptors or recent use is ongoing, administration precipitates abrupt, severe withdrawal within minutes. Patients must be opioid free for about 7 to 10 days (longer for buprenorphine or methadone) before starting naltrexone. Hepatotoxicity is a concern at supratherapeutic doses, not with therapeutic use, so it does not explain this restriction.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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