Pure MOP antagonist used for:

  • Treatment of opioid overdose
  • Reducing constipation
    In combination with PO oxycodone.
Property Drug
Class μ-selective opioid receptor competitive antagonist
Uses Opioid overdose, neuraxial opioid side effects (e.g. pruritus), prevention of constipation in combination with oral opioids
Presentation Clear, colourless solution at
Route of Administration IV, IM, PO
Dosing 0.1-0.4mg Q5min, by infusion
Absorption Very high first pass metabolism leading to ~2% PO bioavailability
Distribution 50% protein bound. VD, highly lipid soluble.
Metabolism Rapid hepatic glucuronidation
Elimination Renal elimination
Resp Reversal of opioid-induced respiratory depression (↑ RR, ↑ VT)
CVS SVR & ↑ BP, arrhythmia due ↑ in SNS tone
CNS ↓ Analgesia, ↓ sedation, ↓ miosis. Antanalgesic in opioid naive patients. Precipitation of opioid withdrawal.
Other considerations Duration of action is ~30-40 minutes is shorter than some opioids, which may lead to re-narcosis if not given subsequent doses or by infusion


  1. Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
  2. Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.
Last updated 2019-07-18

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