Background and Objectives Pruritus induced by intrathecal morphine is a concern in many obstetric patients after cesarean delivery and may detract from the benefit of postoperative pain relief. This study was performed to investigate the efficacy of ondansetron (5-HT₃ receptor antagonist) in treatment of pruritus following intrathecal morphine.

Methods Eighty parturients developing moderate to severe pruritus following intrathecal morphine were randomly allocated into 2 groups. One group received 4 mg ondansetron while the other group received placebo (normal saline). The improvement of pruritus and other adverse effects such as pain scores, nausea, vomiting, sedation, hallucination, and respiratory depression were determined at 30 minutes after study drugs' administration.

Results The treatment success rate was higher in the ondansetron group than in the placebo group (80% v 36%, P < .001). Among the successfully treated patients, the recurrence rates of moderate to severe pruritus within 4 hours after administration of ondansetron and placebo were 12% and 70%, respectively (P < .001). The number of patients with decreased nausea and vomiting score was also higher in the ondansetron group (11 v 1, P < .006).

Conclusion Ondansetron treats intrathecal morphine-induced pruritus after cesarean delivery, particularly in patients suffering from both nausea/vomiting and pruritus.