CRD Summary: The authors concluded that adding montelukast to inhaled corticosteroids (ICS) improved control of mild to moderate asthma, and that salmeterol was at least as effective as montelukast as an add-on therapy, but that montelukast may be safer long term. These conclusions may require some caution in interpretation due to the scarcity of good quality data and heterogeneity between the studies.

CRD Commentary: The objectives and inclusion criteria of the review were clear. Relevant sources were searched for published and unpublished studies, although there was some restriction by language. Steps were taken to minimise the risk of bias and error by having more than one reviewer independently undertake study selection. Multiple reviewers were also involved in data extraction and validity assessment, but it was unclear whether they worked independently. Detailed information was provided about the included studies. Rigorous criteria were used to assess study validity and the results of the assessment were taken into account when interpreting review findings. There was marked heterogeneity in the range of outcome measures reported, though (as the authors noted) the direction of effect showed consistent trends. Appropriate statistical techniques were used to pool the few data suitable for meta-analysis, assess for heterogeneity and explore the effects of differences in study duration and asthma severity. The review was generally well conducted but the authors’ conclusions may require some caution in interpretation due to the scarcity of good quality data and heterogeneity between the studies, which precluded meta-analysis in most cases.