A 28-year-old man on methadone maintenance therapy for opioid use disorder is brought to the emergency department unresponsive with miosis and respiratory rate of 6 breaths per minute. Which feature distinguishes a methadone overdose from that of shorter-acting opioids in terms of clinical management?

• A Naloxone is ineffective against methadone and naltrexone must be used instead
• B Methadone overdose does not cause miosis and the diagnosis should be reconsidered
• C Methadone's long half-life (24–36 hours) necessitates prolonged naloxone infusion or repeated boluses ✓
• D Flumazenil should be co-administered as methadone has benzodiazepine cross-reactivity

Explanation

Methadone has a very long and variable half-life of 24–59 hours, considerably longer than naloxone's half-life of approximately 60–90 minutes. After an initial naloxone bolus reverses respiratory depression, re-narcotisation can occur as naloxone is metabolised. Therefore, patients require either a continuous naloxone infusion at two-thirds of the effective reversal dose per hour or repeated naloxone boluses with extended observation. Naloxone is fully effective at mu-opioid receptors irrespective of the specific agonist.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.