A double-blind randomised trial comparing postoperative analgesia after perioperative loading doses of methadone or morphine

This double-blind randomised study compared postoperative analgesia after a loading regimen of methadone or morphine in thirty women undergoing abdominal hysterectomy. Methadone or morphine, 0.25 mg.kg-1, was given intravenously at induction of anaesthesia with further increments in the recovery room for analgesia if required. The mean (SD) total doses of methadone and morphine required were 0.43 (0.13) mg.kg-1 and 0.45 (0.15) mg.kg-1 respectively. Patients in the methadone group had lower pain scores in the subsequent 48 hours (P less than 0.001) and required less supplementary intramuscular opioids (P less than 0.001). Ten patients in the methadone group did not request any further opioid analgesics while all patients in the morphine group made at least two requests for opioids. The overall postoperative course was remembered as less painful by patients in the methadone group (P less than 0.001). There was no significant respiratory depression or excessive sedation in either group.