Forty-eight randomised controlled trials with 7,793 patients in the ondansetron group and 4,285 in the placebo group, were included. There were 34 studies (n=10,390) of adults and 13 (n=1,688) of children.
The 1 mg dose of ondansetron, although better than placebo, did not have a superior therapeutic effect; the OR was 1.24 (95% CI: 0.97, 1.58) for oral administration and 1.34 (95% CI: 1.04, 1.74) for intravenous administration.
The doses most frequently employed were 4 and 8 mg. Overall, the 4 mg dose of ondansetron was found to be effective; there was no evidence that the drug became more effective at the higher doses.
Early evaluation: for the intravenous administration of ondansetron (4 mg), the OR was 1.77 (95% CI: 1.37, 2.29) and the NNT was 7.91.
Late evaluation: for the oral administration of ondansetron (4 mg), the OR was 1.54 (95% CI: 1.20, 1.97) and the NNT was 10.91.
Late evaluation: for the intravenous administration of ondansetron (4 mg), the OR was 2.91 (95% CI: 2.23, 3.81) and the NNT was 5.72.
The overall percentage for vomiting in the placebo group was 47.87%.
The incidence of headache (35 studies) was 7.05% in the ondansetron group versus 6.16% in placebo group.