REPRODUCIBILITY OF ALLERGEN-INDUCED EARLY AND LATE ASTHMATIC RESPONSES

Background: Constant-dose allergen inhalation challenges are frequentl y used to examine the effect of antiasthma drugs on the allergen-induc ed early and late asthmatic responses. The end-point measurements in s uch studies ave the maximal early and late percent decreases in the fo rced expiratory volume in I second (FEV(1)). Objective: Our purpose wa s to observe the reproducibility and to determine the sample sizes req uired for such studies. Methods: Twenty-eight subjects with allergen-i nduced early and late responses were studied with two constant-dose al lergen challenges separated by 2 to 12 weeks. The early response was m easured as the maximum percent decrease in FEY(1) during the first 2 h ours and the late response as the maximum percent decrease in FEV(1) b etween 3 to 7 hours. Results: The mean +/- SEM early responses were 23 .1% +/- 1.0% and 24.7% +/- 2.0%, whereas the mean late responses were 23.3% +/- 2.0% and 24.5% +/- 2.2%. Reproducibility of measurements wer e such that fewer than eight subjects are required, to show 50% attenu ation of either the early or late response (with 90% power). Conclusio ns: The method of constant-dose allergen challenge is a sensitive tool for detecting changes in early and late asthmatic responses after the use of antiasthma medication.