Timing of ondansetron administration to prevent postoperative nausea and vomiting.

BACKGROUND The original guidelines for using ondansetron recommending its administration prior to induction of anesthesia have been questioned. METHOD In an effort to determine the most effective timing of ondansetron administration to prevent postoperative nausea and vomiting (PONV), a prospective, randomized, double-blind study was performed. Patients undergoing ambulatory plastic surgery procedures estimated to last two hours or more and who had at least two risk factors for PONV (female gender, non-smoker, previous history of PONV and postoperative opioids) participated in the study. General anesthesia for all patients followed the same standard institutional protocol and all patients received dexamethasone 4 mg intravenously at the start of surgery. The control group (n = 188) received 4 mg of ondansetron intravenously prior to the induction of anesthesia. The study group (n = 184) received 4 mg of ondansetron intravenously 30 minutes prior to completion of the surgery. The incidence of PONV during the early (0-2 hours) and delayed (2-24 hours) postoperative periods was recorded. RESULTS No significant difference was found between the groups regarding early postoperative nausea or vomiting (p > 0.05). However, a significant difference (p < 0.05) was noted in both late postoperative nausea (control: 30% vs. study group: 20%) and late postoperative vomiting (control: 17% vs. study group: 8%). CONCLUSION This clinical study indicates that when performing prolonged surgical procedures, late administration of ondansetron (within 30 minutes prior to completing the surgery) is significantly more effective in the prevention of late PONV than when administered prior to the induction of anesthesia.