A randomized, double-blind, placebo-controlled pilot study of IV morphine-6-glucuronide for postoperative pain relief after knee replacement surgery.

Objectives: To determine the dose-response effect of intravenous morphine-6-glucuronide (M6G) on acute postoperative pain.

Methods: Patients undergoing knee replacement surgery under spinal anesthesia were randomly assigned to 1 of 4 single intravenous M6G doses, 0 (placebo), 10, 20, or 30 mg/70 kg, administered 150 minutes after the spinal anesthetic was given. Analgesic effects were evaluated by determining the cumulative patient controlled analgesia (PCA) morphine dose, consumed over a 12 and 24 hours period, after the initial dose of M6G.