Effect of add-on Doxofylline on Lung Function in Stable COPD

Inclusion Criteria: * COPD diagnosis for at least 6 months, according to current European Respiratory Society guidelines * baseline FEV1 ≤ 80% of predicted value * active or former smokers with smoking history ≥ 10 pack-years * patients chronically treated with a long acting muscarinic antagonist (LAMA) and a long acting beta-2 agonists (LABA), in association with or without an inhaled corticosteroid (ICS) * clinically stable disease for 6 months. Exclusion Criteria: * previous or current diagnosis of bronchial asthma * previous lung volume reduction through surgery or endobronchial valves * inability to perform respiratory function tests according to international standards, or contraindications to perform 6-minute walking test * known allergy or intolerance to doxofylline * current or potential pregnancy * mini-Mental test \<21 * congestive heart failure NYHA III or IV * recent (\<6 months) myocardial infarction * unstable arrhythmias * chronic hypotension * active peptic ulcer * severe liver disease * active neoplasia * history of drug or alcohol abuse.