The Effect of High Dose N-acetylcysteine on Airtrapping and Airway Resistance in Chronic Obstructive Pulmonary Disease (COPD) Patients

Background: The mucolytic and antioxidant effects of N-acetylcysteine (NAC) may be of great value in treatment of COPD patients. However, previous studies fail to demonstrate the beneficial effect of NAC. This may be due to insufficient dose of NAC used as well as inadequate outcome parameters measured in the past studies.

Objective of study: This study is to investigate the add-on effect of high dose NAC (600mg tablet twice daily) on reduction of airtrapping and airway resistance in stable COPD patients as well as to study it's effect in reducing exacerbation, improving exercise capacity and quality of life in stable COPD patients.

Study design: Randomized double blinded placebo controlled trial in Kwong Wah Hospital

Methodology: Patients are recruited in Kwong Wah Hospital if they fulfill the spirometric criteria of COPD. Eligible subjects will be randomized into the treatment (NAC 600mg tablet twice daily) and placebo group after completion of run in period. NAC and placebo will be prescribed accordingly in addition to their usual therapy. Both patients and investigators are blinded about the group allocation. Baseline assessment will be done and patients will be followed up at 16th weeks and 52th week of the study.

During each follow-up visit, hyperinflation parameters like inspiratory capacity (IC) will be measured by plethysmography. Airway resistance will be measured by both plethysmography and impulse oscillometry machine. Exercise capacity (6 min walking distance) and quality of life are also recorded during each follow up.

The difference of the above parameters between the 2 groups (drug and placebo group) will be analyszed by the Repeated measures ANOVA test

Inclusion criteria

• Spirometry diagnosed COPD with FEV1/FVC ratio less than 70% and FEV1 less than 80% predicted
• clinically stable and exacerbation free in the past 4 weeks
• history of at least one COPD exacerbation in the past one year

Exclusion criteria

• patients allergic or intolerant to NAC
• Recent use of NAC in the past one month
• history of asthma, non COPD respiratory disorders like bronchiectasis, pneumoconiosis or any active pulmonary infection
• patients on long term steroid
• patients on long term oxygen therapy or non invasive ventilation