A comparison of intrathecal morphine-6-glucuronide and intrathecal morphine sulfate as analgesics for total hip replacement

Postoperative analgesia was assessed after intrathecal administration of morphine-6-glucuronide (M6G) 100 mu g and 125 mu g in 75 patients undergoing total hip replacement. Analgesia was excellent and was similar to that obtained after intrathecal administration of morphine sulfate 500 mu g. Visual analog pain scores recorded postoperatively were low (median = 0) and were similar in all three groups. However, at 6 and 10 h after operation significantly more patients in the M6G 125 group recorded pain as 0 compared with patients in the morphine group (P < 0.04, P < 0.01) and significantly more patients in the M6G 100 group recorded pain as 0 at 24 h after operation compared with patients in the morphine group (P < 0.04). Postoperative meperidine consumption using a patient-controlled system was also similar in each of the three treatment groups. Nausea and emesis occurred frequently in all groups; morphine (nausea 88%, vomiting 76%), M6G 100 mu g (nausea 76%, vomiting 64%), and M6G 125 mu g (nausea 88%, vomiting 60%). Respiratory depression occurred in two and three patients, respectively, in the M6G 100-mu g and 125-mu g groups but did not occur in any patient who received morphine sulfate. The lack of statistical significance in the difference in incidence of respiratory depression between the groups may represent a type II error. However, the risk of late respiratory depression developing after administration of any intrathecal opioid necessitates careful postoperative observation of patients. As M6G is a potent intrathecal analgesic further investigation of this drug using small doses may be useful.