Three doses of intravenous (IV) ondansetron, 1 mg, 4 mg, and 8 mg, wer
e compared to placebo for their antiemetic effect and safety. The drug
s or placebo were administered in a double-blind manner, prophylactica
lly to 589 women undergoing elective outpatient surgical procedures un
der nitrous oxide opioid-based general endotracheal anesthesia. In the
postanesthesia care unit, the number of emetic episodes, periodic ass
essments of nausea severity using an 11-point scale (0 = no nausea; 10
= worst nausea), vital signs, and adverse events were collected by an
independent observer for 2 h. Upon discharge, identical information,
with the exception of vital signs, was collected from the patients' di
ary and via phone call. One pre- and two poststudy blood specimens for
hematology and chemistries were evaluated. During the initial 2 h, pa
tients receiving any dose of ondansetron had significantly better comp
lete response rates (no emesis) than those receiving placebo. Over the
24-h study period, patients who received either 4 mg or 8 mg ondanset
ron continued to have significantly greater complete response rates. A
dverse events were minor, and ondansetron-treated patients had profile
s similar to those of the placebo. Heart rate, blood pressure, respira
tory rate, and laboratory safety variables were not different among th
e groups. Ondansetron did not prolong awakening time. This study indic
ates that ondansetron is a safe and effective prophylactic antiemetic
for women who have outpatient surgery under nitrous oxide opioid-based
general anesthesia.