A patient with severe opioid overdose is given naloxone. The half-life of naloxone is approximately 60–90 minutes. Why must patients be monitored for 4–6 hours after naloxone administration?
- A Naloxone's shorter half-life compared with many opioids (e.g. morphine t½ 2–4 h, methadone t½ 25–55 h) means re-narcotisation can occur as naloxone is eliminated before the opioid ✓
- B Naloxone accumulates in CNS and causes delayed respiratory stimulation
- C Naloxone is converted to an active metabolite with partial agonist properties that masks residual opioid effects
- D Repeated doses of naloxone increase endogenous enkephalin synthesis, worsening CNS depression
Correct answer: A. Naloxone's shorter half-life compared with many opioids (e.g. morphine t½ 2–4 h, methadone t½ 25–55 h) means re-narcotisation can occur as naloxone is eliminated before the opioid
Explanation
Naloxone is a pure competitive mu-opioid antagonist with a plasma half-life of approximately 60–90 minutes—shorter than most opioid analgesics. Once naloxone is eliminated, the opioid (especially long-acting ones like methadone, t½ 25–55 h, or sustained-release formulations) re-occupies opioid receptors, causing re-narcotisation with recurrent respiratory depression ('re-narcotisation'). Extended monitoring or repeated naloxone dosing (or naloxone infusion) is therefore mandatory, particularly with long-acting opioids.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.