Four RCTs (n=490) were included in the review.
Generation of allocation sequence and allocation concealment was adequate in 3 studies and unclear in the fourth; double-blinding was utilised in all studies. Less than 20% of the participants were lost to follow-up in the included studies.
Cessation of vomiting.
There was a greater likelihood of cessation of vomiting during the first hours in the ondansetron group compared with the placebo group (RR 1.33, 95% CI: 1.33, 1.50, p<0.00001; 3 studies, n=466); the NNT was 5 (95% CI: 4, 8). There was no evidence of statistical heterogeneity in this group. However, there were no statistically significant differences between the ondansetron and control groups for cessation of vomiting within 24 hours (RR 1.22, 95% CI: 0.89, 1.67; 2 studies, n=144), but these studies demonstrated significant statistical heterogeneity (I-squared 55.5%).
Intravenous rehydration.
The ondansetron group showed a reduction in the risk of intravenous rehydration in comparison with those in the placebo group (RR 0.42, 95% CI: 0.27, 0.67, p=0.0003; 2 studies, n=359); the NNT was 7 (95% CI: 5, 14). There was no evidence of statistical heterogeneity in this group.
Hospitalisation.
There was no statistically significant risk of hospitalisation in the ondansetron group compared with the placebo group (RR 0.6, 95% CI: 0.2, 1.4; 3 studies, n=466).
Return visit to the ED.
There were no statistically significant differences between groups in terms of return visits to the ED (RR 1.3, 95% CI: 0.8, 2.2).
ORS intake.
There was an increased intake of ORS in ondansetron compared with the placebo group (mean difference 43 mL, 95% CI: 15.5, 70.5; 1 study, n=214)), although the same study showed no significant difference in duration in the ED.
Diarrhoea.
One study showed a significant difference between the ondansetron and placebo groups in the number of episodes of diarrhoeal stools while in the ED, whereas a second study showed no difference (data not reported). Two studies showed significantly more episodes of diarrhoea at the 24-hour follow-up in the ondansetron group compared with the placebo group (data not reported). One trial showed the same effect between the ondansetron and placebo groups at the 48-hour follow-up (data not reported).
Adverse events.
Ondansetron was well tolerated (3 studies, n=345) and adverse events were similar in both groups (data not reported).