A patient is brought unconscious with pin-point pupils, respiratory rate 4/min, and a Glasgow Coma Scale of 6 after suspected fentanyl overdose. Naloxone is administered IV. Which property of naloxone is most relevant to repeat dosing?
- A Naloxone is metabolised by MAO and has a very long half-life of 8–12 hours
- B Naloxone is a partial agonist at mu receptors and may precipitate dysphoria but not reversal
- C Naloxone has a shorter duration of action (~30–90 min) than most opioids, requiring repeat doses or infusion to prevent re-narcotisation ✓
- D Naloxone undergoes extensive renal excretion unchanged and accumulates in renal impairment
Correct answer: C. Naloxone has a shorter duration of action (~30–90 min) than most opioids, requiring repeat doses or infusion to prevent re-narcotisation
Explanation
Naloxone is a pure competitive opioid antagonist with rapid onset but a short duration of action (~30–90 minutes), which is shorter than most opioids including fentanyl and particularly methadone. This means the patient can relapse into respiratory depression after the naloxone wears off — necessitating repeat IV boluses or continuous infusion and close monitoring. Naloxone undergoes extensive hepatic glucuronidation and has poor oral bioavailability.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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