Defining the responder in asthma therapy

In last month’s Journal, Szefler et al presented an article from the National Heart, Lung, and Blood Institute Childhood Asthma Research and Education (CARE) Network on the characterization of response to 2 common therapies for childhood asthma. The article establishes a definition of response as the percent change in prebronchodilator FEV1 7.5%. The importance of the article is that it selected a working definition of response and then attempted to assess whether predictors of response could be determined. The article by Szefler et al takes a systematic look at one definition of response and serves as an example for future discussion of how one characterizes a responder. A limitation in the interpretation of the asthma literature is the inconsistency in the definition of response. The heterogeneity and variability of asthma make it difficult to achieve consensus for this term. This is compounded by the lack of a standardized means to assess asthma control, a measure of response. Should response to an intervention be defined primarily by objective parameters, subjective symptom reports, or a composite measure? Is the observed response to an intervention clinically as well as statistically significant, and how has the choice of primary outcome and sample size influenced these results? In addition, which parameters should be more appropriately thought of as markers of disease severity than measures of response? If these issues are difficult for the specialist and researcher to resolve, how can we provide guidance to our primary care colleagues when they read the asthma literature? The definition of responder is increasingly important as the number of assessment tools multiplies beyond traditional clinical trials to include observational investigations, studies of patients with specific phenotypes