Study of the Effects of High-dose N-acetylcysteine (NAC) in Idiopathic Pulmonary Fibrosis (IPF)

Inclusion Criteria: * Diagnosis of IPF according to the International Consensus Statement * Bronchoalveolar lavage (BAL) showing no features to support an alternative diagnosis. * Patients in whom it was possible to determine single breath DLco. * Patients with newly or previously diagnosed IPF, in whom it was clinically justified to use the standardised regimen azathioprine plus prednisone Exclusion Criteria: * Known intolerance to N-Acetylcysteine. * Patients with respiratory infections at study entry should be excluded until the infections have been treated successfully (VC and Dlco comparable with the values before the infection). * Patients with pre-existing disease that interferes with the evaluation of IPF: extensive old TBC lesions, significant bronchiectasis, moderate or severe COPD. * Patients with malignancy in the last 5 years. If the patient had a malignancy in the past and is free of malignancy for more than five years, the patient is regarded as healed. * Patients with heart failure. * Patients with hepatic function abnormalities contraindicating the use of azathioprine (i.e. clinically significant abnormalities of PTT and/or GGT). * Patients with a renal clearance \< 10ml/min and/or hematuria and/or proteinuria of collagen vascular disease origin. A renal clearance is only performed in the presence of an abnormal serum creatinine and/or serum urea level. * Patients who are artificially ventilated. * Prednisone at a dose \> 0.5 mg/kg/day (or other glucocorticoids such as triamcinolone, dexamethasone or methylprednisolone at an equivalent dose) or azathioprine at a dose \> 2 mg/kg/day during the last month prior to inclusion. * Use of other immunosuppressives (such as cyclophosphamide and colchicine) is not allowed in the last month and for the duration of the trial. * Any form of anticancer therapy or methotrexate are not allowed when used for more than 1 week in the past and for the duration of the trial. * Amiodarone or nitrofurantoin are not allowed in the last 5 years, when used for more than 1 week in the past and for the duration of the trial. * Allopurinol, oxypurinol, thiopurinol, anti-oxidants (e.g. vitamin E) or glutathione supplements are not allowed in the last month and during the trial. * The use of interferon or other antifibrotics (e.g. pirfenidone) is not allowed in the past and during the study. * The use of NAC therapy at a dosage of more than 600 mg/day is not allowed in the last 3 years for a total period of more than 3 months. * Patients suffering or having suffered from documented active ulcer within the last 3 years. * Patients in whom the standardised treatment regimen is contraindicated or not justified. * Pregnancy. * Known or suspected drug or alcohol abuse. * Patients on other investigational compounds or participating in clinical trials on investigational compounds within the last 3 months. * Patients expected to be non-compliant in taking the medication.