The effect of a single intravenous dose of ondansetron in preventing postoperative nausea and emesis (retching and vomiting) (PONV) was investigated in a randomized, double-blind, placebo-controlled, multicentre, international study. Women of ASA class I-III, requiring gynaecological laparotomy, vaginal hysterectomy, or major vaginal surgery were selected for study. Two hundred and thirty-five received placebo, 231 received 1 mg ondansetron, 228 received 8 mg ondansetron and 229 received 16 mg ondansetron, as an infusion over five minutes before the induction of anaesthesia. A standardized balanced anaesthetic technique was employed. This consisted of premedication with either diazepam or temazepam, thiopentone induction, maintenance with nitrous oxide in oxygen supplemented with enflurane or isoflurane, intraoperative analgesia with fentanyl, neuromuscular blockade with any choice of agent and reversal with neostigmine and atropine. Postoperative analgesia was achieved with morphine, and prochlorperazine or metoclopramide were given if a rescue antiemetic was required. A greater percentage of patients in the 8 mg and 16 mg ondansetron groups experienced no postoperative emesis (44% and 39% respectively) than in the placebo and 1 mg ondansetron groups (29% and 28% respectively) for the first 24 hr postoperative period (8 mg vs placebo and 1 mg: P ≤ 0.001; 16 mg vs placebo: P < 0.05; 16 mg vs 1 mg: P < 0.05). Similarly, the percentage of patients who did not experience postoperative nausea were 20%, 26%, 31% and 28% for the placebo, 1 mg, 8 mg and 16 mg ondansetron treatment groups, respectively (8 mg and 16 mg vs placebo P < 0.05). Overall, the incidences of adverse events in the ondansetron and placebo groups were similar. It is concluded that intravenous ondansetron, at doses of 8 mg and 16 mg, is both well tolerated and effective in preventing postoperative nausea and emesis, and no greater benefit was observed with the 16 mg dose in comparison with the 8 mg dose. © 1993 Canadian Anesthesiologists.
