Introduction: Hypotension is the most common side effect of spinal anesthesia. Many interventions, such as administration of intravenous fluids and vasopressor drugs, have been used to minimize or prevent spinal anesthesia-induced hypotension. Animal studies suggest that 5-HT may be an essential factor inducing the Bezold-Jarisch reflex via 5-HT3 receptors in intracardiac vagal nerve endings in the presence of decreased blood volume. The objective of the study is aimed to assess the efficacy of prophylactic intravenous ondansetron in preventing spinal anesthesia-induced hypotension.

Methods: 113 patients were enrolled in the double-blind randomized control trial using a computer random-number generator. They were assigned to either the study (ondansetron) group  or the control (normal saline) group. Prior to the spinal anesthesia, all patients were preloaded with 10 ml/kg of Ringer’s acetate solution. The study group (n=56) received 8 mg of intravenous ondansetron 5 min prior to spinal anesthesia, whereas the control group (n=57) received 4 ml of normal saline solution. In addition, the blood pressure and heart rate were recorded.

Results: Hypotension was presented in 8 patients (14.3%) in the study group and 10 patients (17.5%) in the control group (P=0.636). Bradycardia was observed in 9 patients (16.1%) in the study group; on the other hand, 6 patients (10.5%) in the control group had bradycardia (P=0.385).

Conclusion: Intravenous ondansetron administered 5 min prior to spinal anesthesia does not significant­ly prevent spinal anesthesia-induced hypotension