The primary objective is to demonstrate that CHF 1535 NEXT DPI® (beclomethasone dipropionate + formoterol fumarate 100/6 μg), 1 inhalation twice daily, is non-inferior to the corresponding dose of CHF 1535 pMDI in terms of pulmonary function test (change from baseline to the entire treatment period in average pre-dose morning PEF) in asthmatic adult patients ≥ 18 years under treatment with fixed dose combination of Foster® (beclomethasone dipropionate + formoterol fumarate 100 / 6 μg) 1 inhalation bid.