Placebo-controlled, double-blind, randomized study. Post-infectious bronchiolitis obliterans (PIBO) patients aged 5 years and older of both sexes were enrolled.

Bronchiolitis obliterans (BO) was defined as the presence of signs and symptoms of chronic obstructive lung disease: A) previously documented acute lower respiratory infection (ALRI) with persistence of airway obstruction and respiratory signs and symptoms, such as: dyspnea, tachypnea, retractions, persistent cough, increased antero-posterior diameter of the chest, persistent wheezing, crackles, exercise intolerance; B) findings such as: hyperinflation, atelectasis, and mosaic oligohemia on CT scan; and C) persistent obstructive pattern on pulmonary function test.

Patients were randomly assigned by pharmacy staff in blocks of 4 to receive either capsules of azithromycin 250 mg (Group 1) or placebo (Group 2) 3 days a week for 6 months. Patients whose weight was less than 40 kg received 250 mg 3 days a week (Monday, Wednesday, and Friday) and those weighing more than 40 kg received 500 mg in the same scheme, according to randomization to active drug or placebo. Pulmonary function and number of exacerbations were evaluated. Spirometry and plethysmography were performed at baseline and at 6 months. Variables analyzed were Forced vital capacity (FVC),Flow expiratory volume at the first second (FEV1), Total lung capacity (TLC),Residual volumen(RV),especific conductance (sGaw). Patients had been clinically stable over the previous three weeks.

Inclusion Criteria:

• Patients with diagnosis of Bronchiolitis obliternas
• older than 5 years
• Ability to perform pulmonary function test

Exclusion Criteria:

• Not being able to perform lung function study adequately
• Other causes of chronic lung disease (bronchopulmonary dysplasia, cystic fibrosis, primary or secondary immune deficiency)
• Previous history of portal hypertension, liver cirrhosis, splenomegaly or chang in normal values of laboratory at the start of the study.
• History of hypersensitivity to macrolides

Patients were randomly assigned by pharmacy staff in blocks of 4