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Inhibition of Epidural Morphine-induced Pruritus by Intravenous Droperidol: The Effect of Increasing the Doses of Morphine and of Droperidol

Background and Objectives Because the mechanism of inhibition of epidural morphine-induced pruritus by droperidol is not clear, this study was undertaken to determine the effects of larger doses of droperidol or morphine, or both. Methods A double-blind study was performed in 210 ASA I or II patients undergoing cesarean delivery, who were randomly assigned to six groups. All patients received epidural anesthesia with 0.5% bupivacaine containing 1:200,000 epinephrine, to which 2 mg (groups 1, 2, and 3) or 4 mg (groups 4, 5, and 6) morphine sulfate was added. Just after delivery, 2.5 mg droperidol was given intravenously to groups 2 and 5, and 5 mg was given to groups 3 and 6. During the postoperative period, the patients were assessed for the occurrence and severity of pruritus (classified as absent, mild, moderate, or severe) or other untoward symptoms. The groups were compared for the incidence of pruritus by the Mann-Whitney nonparametric test. Results The incidence of pruritus was significantly reduced only when the control group (no droperidol) was compared with the group that received 2.5 mg droperidol, both when 2 mg and when 4 mg morphine was used. A 5-mg dose of droperidol had no inhibitory effect. There was no difference in the incidence of pruritus between use of 2 mg and 4 mg morphine. Other untoward effects of morphine either could not be observed or occurred with an incidence unaffected by either dose of droperidol. Conclusion Pruritus caused by epidural use of 2 or 4 mg of morphine is inhibited by the intravenous use of 2.5 mg droperidol but not by a larger dose.