Advair 115/21 MDI for Asthma

The objectives of this study are to measure Impulse Oscillometry (IOS) in patients with asthma extensively at baseline in patients with mild-to-moderate asthma, treated with as-needed short acting beta agonist only, to measure respiratory resistance and small airway dysfunction accurately and precisely at baseline, from which to measure onset of action of Advair MDI in comparison with that of Symbicort MDI. Initial screening will assess IOS resistance and small airway dysfunction and its response to short acting beta agonist (SABA). Patients will be selected from among those who manifest a 40% improvement in small airway function assessed by IOS low frequency reactance after SABA compared to baseline. After screening, patients will be randomized to receive either Advair or Symbicort; and will be assessed at randomization before and at several intervals after initial dosing, up to 4 hours. Patients will return again 4 weeks after randomization for extended IOS (and spirometry) testing as done at randomization.