Effect of High/Low Dose N-Acetylcysteine on Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-analysis

Background: Chronic obstructive pulmonary disease (COPD) is a leading cause of mortality and morbidity worldwide, charcterised by persistent airflow limitation, mucus hypersecretion, oxidative stress and airway inflammation. N-acetylcysteine (NAC) have anti-oxidant and anti-inflammatory properties, which have been shown an uncertain benefit in COPD patients. Method: Systematic searches were conducted in Cochrane, Medline and Embase electronic databases. A meta-analysis was performed to evaluate the different effect between high and low-dose NAC treatment on COPD exacerbation. Results: This review yielded 11 studies. The methodological quality of included studies were scored using the Jadad score, with a scale of 1 to 5 (score of 5 being the highest). Data showed high-dose NAC can reduce both the total number of exacerbations (RR = 0.59, 0.47 to 0.74, 95%CI, p < 0.001) and the proportion of patients with at least one exacerbation (RR = 0.76, 0.59 to 0.98, 95%CI, p = 0.03). In the low-dose group, subgroup with jadad <= 3 showed a significant decrease (RR = 0.69, 0.61 to 0.77, 95%CI, p < 0.001) in the proportion of patients with exacerbation, the other subgroup with Jadad score > 3 showed no significant decrease (RR = 0.98, 0.90 to 1.06, 95%CI, p = 0.59). And low-dose NAC showed no benifit in the total number of exacerbations (RR = 0.97, 0.68 to 1.37, 95%CI, p = 0.85). Neither high nor low-dose NAC treatment showed benifit in forced expiratory volume in one second(FEV1)(WMD = 1.08, -9.97 to 12.13, 95%CI, p = 0.85). Conclusion: Long-term high-dose NAC treatment may lead to a lower rate of exacerbations. But the effect of low-dose NAC treatment remains uncertain. Further researches are needed to confirm this outcome and to clarify its mechanisms.