A randomized, double-blind, dose-response study of ondansetron in the prevention of postoperative nausea and vomiting

To determine the dose-response relationship of ondansetron in preventing postoperative nausea and vomiting (PONV) in women undergoing elective surgery.

Prospective, randomized, double-blind study.

University-affiliated hospital.

175 women aged 18 to 80 years scheduled for elective surgery.

One of six doses of ondansetron (0.5 mg, 1 mg, 2 mg, 4 mg, 8 mg, 16 mg) or placebo was given prior to the induction of general anesthesia with propofol. Maintenance was with nitrous oxide, isoflurane, opioid, and muscle relaxant.

The study period began when the patient emerged from anesthesia. Nausea scores were recorded on a 0 to 10 scale at multiple time points during the 24-hour study period. Patient satisfaction via a visual analog scale (VAS) was determined at 1 and 24 hours after awakening. Rescue medication was given for severe nausea, three emetic episodes within 15 minutes, or if requested by the patient. The primary efficacy variable was the need for rescue antiemetic therapy. The dose-response curve (by logistic regression) of the percentage of patients not rescued versus dose indicated an ED50 of 0.54 mg (95% confidence interval 0.03-1.05 mg). Fewer patients required rescue in the 4 mg dose group compared with lower doses. However, the difference reached significance only in comparison with the 0.5 mg dose group. Survival analysis of the need for rescue, and nausea score versus time curves, also both suggested the superiority of the 4 mg dose compared with lower doses. In addition, there was a highly significant correlation between the lack of need for rescue and satisfaction with anesthesia at 24 hours after emergence.

The recommended dose of ondansetron for PONV prophylaxis in women remains 4 mg.