Comparison of Ondansetron with Gabapentin for prevention of intrathecal morphine induced pruritus

Background: Ondansetron has been used successfully for prophylaxis and treatment of intrathecal morphine induced pruritus. Gabapentin has anxiolytic, antiemetic, antipruritic effects and has also been shown to potentiate the analgesic effect of intrathecally or epidurally administered opioids. Materials and method: We compared the effectiveness of oral gabapentin with intravenous ondansetron to prevent incidence of intrathecal morphine induced pruritus. In a prospective, double-blind study, sixty patients aged 18-65 years with ASA physical status I and II undergoing surgery under subarachnoid block were randomized to receive placebo tablets (ondansetron group) or gabapentin 1200 mg (gabapentin group) 2 hours before surgery. Patients receiving placebo tablets received 8 mg of intravenous ondansetron and those receiving gabapentin received 4 ml of intravenous normal saline just prior to subarachnoid block with 3 ml of 0.5% hyperbaric bupivacaine plus 0.2 mg morphine. The incidence, onset, severity, location of pruritus and incidence of side effects were studied for next 24 hours. Results: The overall incidence of pruritus was 48.3%. The incidence, severity, location of pruritus was comparable between the two groups. There was significant difference between the onset of pruritus between groups (p=0.009). The incidence and grade of nausea vomiting, requirement of intraoperative sedation was comparable between groups. The incidence of urinary retention was significantly high in gabapentin group (p=0.020). Respiratory depression was observed in one patient. Conclusion: A single dose of 1200 mg oral gabapentin 2 hours before, is as effective as prophylactic intravenous ondansetron 8 mg for prevention of intrathecal morphine induced pruritus.