Epidural naloxone reduces pruritus and nausea without affecting analgesia by epidural morphine in bupivacaine

Purpose: To determine whether epidural naloxone preserved analgesia while minimizing side effects caused by epidural morphine. Methods: Eighty patients undergoing combined epidural and general anesthesia for hysterectomy were randomly assigned to one of four groups. All received 2 mg epidural morphine bolus one hour before the end of surgery and a continuous epidural infusion was started containing 4 mg morphine in 100 mi bupivacaine 0.125% with either no naloxone (Group 1, n=20), 0.083 mu g.kg(-1)hr(-1) of naloxone (Group 2, n=20), 0.125 mu g.kg(-1).hr(-1) of naloxone (Group 3, n=20) or 0.167 mu g.kg(-1).hr(-1) of naloxone (Group 4, n=20). Analgesia and side effects were evaluated by blinded observers. Results: The combination of epidural morphine and bupivacaine provided good analgesia. Eight hours after the end of surgery, the pain score in the group receiving the highest dose of naloxone was lower than in the control group (VAS 1.2 vs 2.0, P < 0.05) but there was less pruritus in the high-dose naloxone group (itching score 1.3 vs 1.9, P < 0.05). Pain scores were no different in any of the naloxone groups from the control group. Itching was less in both of the higher dose naloxone groups (P < 0.05 at 8,6, and 32 hours). The incidence of vomiting in the control group was 40% vs 5% for high dose naloxone group (P < 0.05). Conclusions: Epidural naloxone reduced morphine-induced side effects in dose-dependent fashion without reversal of the analgesic effect.