To compare the efficacy of prophylactic intravenous ondansetron versus dexamethasone on the incidence and severity of pruritus among patients receiving intrathecal fentanyl & 0.5% Hyperbaric Bupivacaine for infra-umbilical surgery.

It is a hospital based randomised, double-blind, clinical trial. 100 ASA grade I–II patients receiving intrathecal 2.5ml of 0.5% hyperbaric bupivacaine and 25 micrograms of fentanyl were randomized to receive ondansetron 8 mg IV(n=50) or dexamethasone 8mg IV(n=50) before the commencement of spinal anesthesia. Patients were evaluated for presence & severity of pruritus every 15 min in the first hour and at 2, 3, 4, 5, and 6 h after administration of spinal anaesthesia using Numerical rating scale. Patients with NRS score >3 received 10mg Chlorpheniramine slow IV as rescue drug. Statistical analysis was performed using Chi square tests and Student’s t-test, as appropriate.

Overall incidence of pruritus was significantly reduced in the ondansetron group as compared to dexamethasone group (68% versus 32%) with P < 0.005.Time of onset & duration of pruritus was however similar in both groups.

Prophylactic ondansetron is more efficacious than dexamethasone in prevention of intrathecal fentanyl induced pruritus. However Dexamethasone & ondansetron are equally effective in prophylaxis against PONV caused by intrathecal fentanyl.