Effect of Vilanterol on Methacholine Challenge Results

This will be a double-blind, three-way crossover study comparing combination vilanterol+fluticasone with fluticasone monotherapy and a placebo (vilanterol is not available as a monotherapy). The order in which the treatments are given will be randomized and each treatment will be separated by a minimum one-week washout. Fifteen asthmatic participants will be recruited from the local community. Methacholine challenge testing (MCT) with the two-minute tidal breathing protocol will be used to quantify the bronchoprotective effects (if any) of each treatment against methacholine-induced bronchoconstriction. Each participant will undergo a total of nine methacholine challenges. After a baseline methacholine challenge, the randomized treatment (identity unknown to investigator or participant) will be administered through an Ellipta® (multi-dose dry powder inhaler). Thirty minutes following treatment administration, a second methacholine challenge will be performed. At 24 hours post-treatment, each participant must re-visit the lab for one methacholine challenge. The same process will be followed for each treatment.