Chronic obstructive pulmonary disease (COPD) is a condition defined as a disease state characterized by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and is associated with an abnormal inflammatory response of lungs to noxious particles or gases, primarily caused by cigarette smoking. The accelerated decline in lung function is closely associated with an increased number of neutrophils in the sputum and hence with higher level of airway inflammation. It becomes clear that the inflammatory process potentiates as COPD progresses and exerts damage which is irreversible. Oxidative stress is inextricably linked to the inflammatory response.

There is increasing evidence that an oxidant/antioxidant imbalance, in favor of oxidants, occurs in COPD.

NAC has been reported to reduce the viscosity of sputum in both cystic fibrosis and COPD, facilitating the removal of pulmonary secretions. Moreover, by maintaining the airway clearance, it prevents bacterial stimulation of mucin production and hence mucus hypersecretion.

The superiority of NAC over the other mucolytics may be in its anti-inflammatory and antioxidant properties and its mucolytic actions.

The aim of this study is to evaluate the effects of treatment with NAC long on oxidative stress marker change and also explore the effect of NAC to airway inflammatory, lung function test and CAT scores. Selected oxidative stress marker was defined as 8 - isoprostane, protein carbonyl, DNA damage.

Inclusion Criteria:

• Eligible stable COPD patients who are currently treated with only short-acting bronchodilator (salbutamol or fenoterol/ipratropium bromide) or long-acting bronchodilator (LABA or LAMA) or inhaled corticosteroids/LABA
• Pre-bronchodilator FEV1 ≥ 80% and < 80% predicted
• Current or ex-smokers (≥ 10 pack year)

Exclusion Criteria:

• Concomitant with active and old pulmonary TB, lung cancer, bronchiectasis, lung fibrosis, destroyed lung and other malignancies
• Recent acute coronary syndrome (within 12 weeks)
• Cerebrovascular disease without neurological recovery
• Cognitive impairment
• Recent acute exacerbation of COPD (within 4 weeks)
• Recent respiratory viral infection (within 4 weeks)
• Could not provide adequate sputum specimens
• Develop worsening of COPD symptoms during sputum induction
• Could not provide informed consent