Repeatability of allergen-induced airway inflammation

Background: Allergen inhalation challenge is a useful clinical model to inv estigate the effects of asthma therapies on allergen-induced airway respons es; however, the repeatability of allergen-induced airway inflammation is n ot known. Objective: The purpose of this study was to investigate the repeatability o f allergen-induced increases in sputum eosinophils. This information will a llow the prediction of the number of subjects required in studies evaluatin g asthma therapies. Methods: Seventeen subjects completed 2 allergen challenges using the same dose of allergen, at least 3 weeks apart. Allergen-induced airway responses were measured for 7 hours after challenge. Differential cell counts from i nduced sputum were determined the day before and 7 and 24 hours after chall enge; methacholine PC20 was measured the day before and 24 hours after chal lenge. Results: The intraclass correlation coefficient for maximum percent late fa ll in FEV1 was 0.32 and for the area of the late response was 0.61. The sam ple size predicted to be necessary to observe 50% attenuation of the maximu m percent late fall in FEV1 and the late area under the curve with a power of 0.95 was 9 subjects. The intraclass correlation coefficient for percent of allergen-induced sputum eosinophils was 0.60 at 7 hours and 0.53 at 24 h ours after challenge. With a randomized cross-over study design, the sample size predicted to be necessary to observe 50% attenuation of allergen-indu ced percent of eosinophils with a power of 0.95 was 5 subjects. Conclusion: Allergen inhalation challenge with measurements of sputum eosin ophils is a noninvasive and reliable method for evaluating the anti-inflamm atory effects of asthma therapies.