A Study in Patients With Asthma

Inclusion Criteria: * Male or female outpatients aged ≥ 18, who have signed an Informed Consent form prior to initiation of any study-related procedure. * Clinical diagnosis of asthma for a minimum of 12 months prior to screening confirmed by a chest physician according to international guidelines (GINA). The evidence of asthma must be confirmed through a documented (in the last three years) positive response to the reversibility test, defined as ΔFEV1 ≥ 12% and ≥ 200 mL over baseline, within 30 minutes after administration of 400 μg of salbutamol pMDI or through a documented (in the last three years) positive response to methacholine challenge test (PC20 \< 8 mg/mL or PD20 \< 1 mg). * Baseline FEV1 \> 80% of the predicted normal value after appropriate washout from bronchodilators (to be checked at screening and at randomisation visits). * Asthma Control Test score ≥ 20 and \< 25 (to be checked at screening and at randomisation visits). * Impaired small airways function defined as baseline peripheral airway resistance \[R(5Hz)-R(20Hz)\] ≥ 0.07 kPa/L/s (to be checked at screening and at randomisation visits). * Patients on previous regular treatment with Seretide® Accuhaler® (fluticasone propionate 250 μg plus salmeterol xinafoate 50 μg per actuation, daily dose of fluticasone 500 μg plus salmeterol 100 μg) at a stable dose for at least 2 months prior to inclusion. * A cooperative attitude and ability to be trained to the proper use of DPI. Main Exclusion Criteria: * Patients with a diagnosis of COPD according to GOLD guidelines. * Current smokers with a smoking history of \> 10 pack/year. * Patients who have a clinical or functional uncontrolled respiratory, haematological, immunologic, renal, neurologic, hepatic, endocrinal or other disease, or any condition that might, in the judgment of the investigator, represent for the patients an undue risk or that could compromise the results or interpretation of the study. * History or current evidence of uncontrolled heart failure, clinically relevant coronary artery disease, recent myocardial infarction, severe hypertension, uncontrolled cardiac arrhythmias. * Patients treated with LABA or ICS/LABA fixed combination in the 24 hours before the screening visit. * Severe asthma exacerbation leading to intake of systemic corticosteroids (\> 10 days) in the month before the screening visit.