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Combination Antiemetics: What Is the Evidence?

Although a number of therapies are available for the management of postoperative nausea and vomiting (PONV), none is entirely effective. Currently, the overall incidence of PONV for all surgeries and patient populations is estimated to be 25% to 30%. In certain high-risk patients, this incidence is as high as 60% to 70%. Furthermore, it is estimated that approximately 0.18% of all patients may experience intractable PONV, leading to a delay in hospital discharge and unanticipated hospital admissions. The number needed to treat (NNT) is a useful way of looking at the efficacy of different antiemetics. A NNT of 4 or less represents a clinically relevant effect. The NNT of some antiemetics that have been studied in systematic reviews is shown in Table 1. The 5-HT3 receptor antagonists are considered to be effective antiemetics with an acceptable side effects profile. Ondansetron was the most commonly studied member of this group. In a meta-analysis of randomized controlled trials involving ondansetron, the best NNT to prevent PONV with the best documented regimens was between 5 and 6. This means that six patients had to be exposed to ondansetron to prevent PONV in one who would have vomited or been nauseated had he or she received placebo, a somewhat disappointing result. Another effective antiemetic is droperidol. It has been suggested that droperidol may be the most cost-effective first-line antiemetic agent, although recently its safety has been questioned. The NNT to prevent early nausea was 5 and to prevent vomiting was 7. A single dose of dexamethasone has been reported to be effective for PONV prophylaxis without evidence of significant side effects. It has also been suggested that dexamethasone might be especially effective against late PONV. The NNT to prevent early and late vomiting compared with placebo was 7.1 and 3.8, respectively. For late nausea, the NNT was 4.3.