Efficacy of 5-HT3 receptor antagonists in radiotherapy-induced nausea and vomiting: a quantitative systematic review

CRD COMMENTARY: This is a clearly presented review with well-defined inclusion criteria. A reasonable search for published literature was carried out which was not limited by the language of publication. No specific attempts were made to locate unpublished data however and abstracts were excluded. There is therefore a possibility of publication bias. In addition no details were reported about methods used to select studies and extract data. The number of individuals involved in these processes was also not stated. No data was presented on the validity of the included studies and it would appear that no formal assessment was performed. Despite this the authors do make recommendations about study quality in their concluding remarks. However RCTs were included in the review and so the data are probably reasonably robust. The authors present the effectiveness findings without combining the data from different studies due to differences between the studies. However, the authors do make assumptions about the similarity of different 5-HT3 antagonists and different controls when they combine adverse effects data on headaches across studies (i.e. combining control and treatment arms across studies to estimate an overall effect). This also has the effect of breaking the randomisation within the studies and is not an appropriate method for pooling, so these findings should be treated with great caution. In addition the data are presented as NNTs and NNHs in the abstract, although RRs are also presented in the results. RRs are the more reliable estimate of effect size across different studies. If the studies being pooled vary in their baseline risk and outcome frequency, to report NNTs and NNHs could be misleading. This should be borne in mind when interpreting the findings in terms of NNTs and NNHs. Overall, given the problems outlined above the overall findings and conclusions of the review should be treated with great caution.