Immunotherapy for asthma: unfavorable studies

Introduction: Many studies have demonstrated efficacy of immunotherapy (IT) for asthma. Two meta-analyses reached the same conclusion. Because some st udies failed to demonstrate efficacy, it is instructive to review reasons w hy that may have been the case. Methods: Two meta-analyses were used to identify studies that did and did n ot demonstrate efficacy. These were reviewed to identify the sources of var iability. Results: Most studies are able to demonstrate a treatment effect of IT alth ough they have wide confidence intervals. The studies were heterogeneous wi th respect to selection of subjects, underlying populations, the main treat ment protocol, concomitant treatments, the duration of treatment and follow up, and the effect of the protocol on concurrent treatment. There were also problems with the blinding. In most cases, it was difficult to determine h ow the doses of extract given compared between studies. Conclusions: Studies that fail to demonstrate a treatment effect of IT may do so for many reasons. Given the heterogeneity of IT clinical trials as a group, it is not surprising that variable results occur. The use of multipl e studies in a meta-analysis with its underlying assumption of homogeneity is problematic.