Oliver Pfaar

Background The symptoms of house dust mite (HDM)‐induced allergic rhinitis (AR) vary with changes in exposure related to the weather or the domestic environment. In allergen immunotherapy (AIT) studies, a certain level of AR disease activity is necessary to demonstrate treatment efficacy; the latter can be underestimated if a substantial proportion of the patient population is weakly symptomatic. Objective To better estimate the real treatment effect of a HDM sublingual AIT (SLIT) tablet, we analysed the results of natural field studies in detail by applying a tertile approach. Methods We used data from three randomised, controlled trials (RCT) in a total of 2585 patients with AR treated with the 300 index of reactivity (IR) HDM SLIT‐tablet or placebo. The study centres were grouped into tertiles according to the level of combined symptom and medication scores in patients in the placebo group. In each tertile, the difference between SLIT and placebo was assessed through an analysis of covariance. Results In the three RCTs, combined scores were found to be similar in the SLIT and placebo groups in the low tertiles. The treatment effect of the 300 IR HDM tablet increased in the medium and high tertiles, with notably significant differences versus placebo in the highest tertile and greater (ranging from −21% to −39%) than in the entire study population (−13% to −20%). The positive relationship between treatment efficacy and the combined score in each tertile was independent of the RCT and the score used. Conclusion and Clinical Relevance Application of the tertile approach to AIT studies in a field in which many variables interact strongly might provide more accurate and meaningful measurements of efficacy and benefit for patients, better reflecting their real‐life condition.