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Updated: Apr 27, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
07:23

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

Published on: July 29, 2014

34.7K

Morphine-6-glucuronide is responsible for the analgesic effect after morphine administration: a quantitative review

R Klimas1, G Mikus2

  • 1Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.

British Journal of Anaesthesia
|July 3, 2014
PubMed
Abstract

Insights

Morphine-6-glucuronide (M6G) significantly contributes to morphine

Area of Science:

  • Pharmacology
  • Neuroscience
  • Drug Metabolism

Background:

  • Morphine-6-glucuronide (M6G) is a potent µ-receptor agonist.
  • M6G's contribution to morphine's analgesic effect is not fully understood.

Purpose of the Study:

  • To quantify the relative contribution of M6G and morphine to analgesia.
  • To compare M6G and morphine effects across different administration routes.

Main Methods:

  • Utilized published data on receptor binding and drug concentrations (AUC).
  • Calculated free cerebrospinal fluid (CSF) concentrations, corrected for receptor binding and potency.
  • Compared M6G and morphine contributions to overall analgesic effect.

Main Results:

  • M6G accounts for the majority of morphine's analgesic effect (85-96%) across routes.
  • In renal insufficiency, M6G causes ~97.6% of oral morphine's analgesic effect.
  • Morphine acts as a prodrug due to M6G accumulation in renal impairment.

Conclusions:

  • M6G, not morphine, is the primary driver of analgesia.
  • Patient renal function is critical for optimizing morphine dosage.
  • M6G's role highlights the importance of metabolite activity in drug efficacy.
Keywords:
analgesiamorphinemorphine metabolismmorphine pharmacokinetics

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