The study will be a five-period cross-over study with each 7 day treatment period separated by a 7 day wash-out period. The study will enroll asthmatic subjects ≥18 years of age who are currently receiving inhaled corticosteroid treatment with an FEV1 of between 40-85% of predicted normal and with airway reversibility as demonstrated by an increase in FEV1 of ≥12% and ≥200ml .