Oral ondansetron in the prevention of postoperative nausea and vomiting.

The effect of three times daily oral ondansetron in preventing postoperative nausea and vomiting was investigated in two randomized, double-blind, placebo-controlled, multi-centre studies. The first study compared ondansetron 1, 8 and 16 mg to placebo, and the second study compared 8 mg ondansetron to placebo. Both studies included ASA Class I-III female patients about to undergo major abdominal gynaecological surgery or vaginal hysterectomy. In the first study, the 8 and 16 mg ondansetron groups had a significantly lower incidence of nausea and vomiting in the 0-24 h period following recovery from anaesthesia than the placebo group. Ondansetron 8 mg three times daily was also significantly better than placebo in the second study. Side-effects mainly consisted of constipation, headache, and asymptomatic elevation of liver enzymes. The incidence of side-effects was similar in ondansetron- and placebo-treated patients. There appeared to be no clinically important benefit of the 16 mg three times daily ondansetron regimen over the 8 mg three times daily dose, therefore 8 mg three times daily is recommended as the optimal oral dose in the prevention of postoperative nausea and vomiting.