The study will consist of two parts. Part A is a parallel group, placebo-controlled single dose study to ascertain the Pharmacokinetics (PK) profile, safety and bronchodilator effect of a single dose of RPL554 administered via pMDI. Five of the 6 treatment arms will be double-blind and one will be single-blind (due to the different number of capsules administered). Part B is a 7-day placebo-controlled, complete block cross-over, repeat dose study to assess the bronchodilator effect of repeat doses of RPL554 delivered via pMDI.
