Chronic Airway Disease, Mucus Rheology and Exacerbations

Inclusion Criteria: * Subjets between 40 - 85 years (included) * Written and signed informed consent form * Subjects must be able to attend all planned visits and comply with all test procedures * Beneficiary of or affiliated with the French social security system * Man or woman with chronic obstructive pulmonary disease for at least 1 year defined according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria and validated by the clinical investigator * Optimal treatment according to GOLD class severity C or D recommendations * \>=3 exacerbation (regardless of severity: mild-moderate-severe) or ≥ 1 severe exacerbations (requiring hospitalization) in the past 12 months * Spontaneous or induced sputum production * Electrocardiogram: corrected distance between Q and T waves (QTC) \<450 ms in men, QTC \<470 ms in women * Normal audiogram for age or absence of contraindication to azithromycin for long course according to Oto-Rhino-Laryngological specialist opinion Exclusion Criteria: * Pregnancy or breastfeeding * Patients who are prisoners or under other forms of judicial protection * Patients under any form of guardianship * Participation in another interventional protocol, (current or during the month preceding inclusion) * Received azithromycin in the past 3 months * Patient whose primary diagnosis is bronchial dilation based on CT scan documentation * Known hypersensitivity to azithromycin, erythromycin, any other macrolide, ketolide or any of the excipients of the azithromycin-based specialty used * Concomitant use of medication contraindicated with azithromycin (dihydroergotamine, ergotamine, cisapride, colchicine) * Other respiratory diseases or associated lung infections * Severe hepatic insufficiency and severe cholestasis (a liver biological test will be carried out if clinical suspicion) * Renal impairment with creatinine clearance \< 40 mL/min * Patients with hematological malignancies who have undergone allogeneic hematopoietic stem cell transplantation * Patients with galactose intolerance, Lapp lactase deficiency or glucose or galactose malabsorption syndrome (rare hereditary disease) due to the presence of lactose in the specialty Zithromax.