Background: The aim of this study was to compare the efficacy of ondansetron, Midazolam and metoclopramide with placebo in preventing PONV following strabismus surgery.

Material and Methods: 160 patients were allocated with simple randomization in 4 groups of 40: group ON received Ondansetrone 0.05mg/kg, MT group received Metoclopramide 0.15mg/kg, MD group received Midazolam 0.03mg/kg intravenously and group CT received the solution of NaCl 0.9% as placebo infused with the same volume and the same manner 30 minutes before the end of surgery. The patients were evaluated for nausea, vomiting, need and  dosage of anti-emetic drugs, time of liquid and solid diet tolerance, drug complications and satisfaction score for the initial 24 hours after anesthesia.

Results:  The frequency of nausea (p-value = 0.001< 0.05) and vomiting (p-value=0.084>0.05) was lower in ON group and both of these complications were lower in MD group compared with MT and CT group. Use of rescue antiemetic was higher in MT and CT group (p-value = 0.001 < 0.05). Patient satisfaction was higher in ON group compared with other 3 groups (p-value=0.001<0.05).

Conclusion:   Prophylactic use of Ondansetron is more effective with fewer side effects than Metoclopramide and Midazolam in the prevention of PONV following strabismus surgery. Furthermore, metoclopramide was less effective and was associated with more adverse effects.