A Study to Compare the Relative Potency of Salbutamol Administered Via Metered Dose Inhalers (MDI) Containing Propellants HFA-152a to HFA-134a in Mild Asthmatics Aged 18 to 65 Inclusive

The primary objectives of the study are:

Part 1: to characterize the potency and variability of dose response on efficacy (Provocative concentration of methacholine causing at least a 20% fall in forced expiratory volume (FEV1) [PC20]) of salbutamol administered via MDI with salbutamol HFA-134a or salbutamol HFA-152a in participants with mild asthma.
Part 2: to compare the comparative dose response on efficacy (PC20) of salbutamol when administered via MDI with salbutamol HFA-134a or salbutamol HFA-152a in participants with mild asthma.