Background: In contemporary medicine, morphine remains the drug of choice in the treatment of severe postoperative pain. Nevertheless, morphine has several side effects, which can seriously compromise its analgesic effectiveness and the patient safety/compliance. The search for opioid analgesics with a better side-effect profile than morphine has led to a morphine metabolites, morphine-6-glucuronide (M6G).
Objective: The objectives of the current paper are to give an overview of the analgesic properties of M6G, assess the dose range at which it produces equianalgesia to morphine and explore its side-effect profile.
Methods: A review of published clinical studies (Phase II - III) on M6G in the treatment of experimental and clinical pain is given.
Results/conclusions: M6G > 0.2 mg/kg is an effective analgesic with a slower onset but longer duration of action (> 12 h) compared with morphine. Side effects, most importantly postoperative nausea and vomiting, occur less frequent after M6G treatment. M6G is an attractive alternative to morphine in the treatment of severe postoperative pain.