Introduction Hypotension is the most common complication after subarachnoid anesthesia for cesarean delivery. Several therapeutic and preventive measures are used to attenuate this side effect. Serotonin receptor–blocking drugs have been suggested as one such approach. We sought to determine whether prophylactically administered intravenous ondansetron could attenuate hypotension in patients undergoing elective cesarean delivery performed under subarachnoid anesthesia.

Methods Eighty-six patients undergoing elective cesarean delivery were recruited and randomly allocated to receive either 8 mg intravenous ondansetron (group O; n = 44) or placebo (group P; n = 42) in a prospective double-blind design. Systolic blood pressure (SBP), mean arterial pressure (MAP), diastolic blood pressure (DBP), and heart rate (HR) were measured at baseline and at 3-minute intervals from the time of initiation of subarachnoid anesthesia until delivery. Ondansetron effect on hemodynamics (SBP, DBP, MAP, and HR) was quantified and analyzed using a linear mixed effect model.

Results We did not find differences in SBP (P = 0.78), MAP (P = 0.89), DBP (P = 0.82), or HR (P = 0.18) between the 2 groups during the study period. Phenylephrine requirements to treat hypotension were 350 μg (175–700 μg) in group O and 450 μg (300–700 μg) in group P (P = 0.30). The incidence of pruritus was 63% (n = 28 of 44) in group O and 56% (n = 23 of 42) in group P (difference, 0.08 [95% confidence interval, −0.23 to 0.41], P = 0.59). No difference in the incidence of nausea and vomiting or sensory level was found.

Conclusions Ondansetron premedication does not attenuate hemodynamic changes after subarachnoid anesthesia nor does it reduce the amount of vasopressor use, pruritus, or nausea and vomiting.