Two RCTs were included, with a total of 612 patients. The trials were judged to be good quality, but one of them did not state the method of randomisation. The trial authors had difficulties recruiting patients and thus the trials had power deficits.
In the trial using intravenous ondansetron in patients with acute or chronic pain (n=520 patients), both 8mg and 16mg of ondansetron were more effective for complete control of vomiting than placebo, while only the 16mg dose was more effective for complete control of nausea. There was no significant difference between the two doses in terms of control of vomiting. There was no significant difference in pain between the groups and patient satisfaction was better with ondansetron than with placebo.
In the trial of oral ondansetron in patients with cancer pain (n=92) there was no significant difference between ondansetron, metoclopramide, or placebo in control of vomiting or nausea, or in requirement of rescue anti-emetics. Similarly, there was no significant difference in pain scores or satisfaction between groups.
Overall, the pooled data showed significantly more complete control of vomiting at 24 hours with ondansetron (OR 2.21, 95% CI 1.59 to 3.08), more complete control of nausea (OR 2.19, 95% CI 1.26 to 3.81), and less need for rescue anti-emetics (OR 0.48, 95% CI 0.34 to 0.69). The incidence of adverse events was low and comparable to placebo. The most common adverse events were headache and dizziness. There was no statistically significant heterogeneity.