N-acetylcysteine and exacerbations of chronic obstructive pulmonary disease.

Oxidative stress may play a role in chronic obstructive pulmonary disease (COPD) exacerbations. There is heterogeneity in the literature with regard to the impact of antioxidant therapy on COPD exacerbation frequency. Clinical trials of N-acetylcysteine in COPD were identified in unrestricted searches of MEDLINE, CINAHL, International Pharmaceutical Abstracts and the Cochrane Register. Randomized, controlled trials which reported exacerbations over a treatment period > or =3 months were selected. Two observers independently extracted data regarding exacerbation number over the treatment period in subjects allocated to either N-acetylcysteine or placebo. Data were analyzed using inverse-variance weighted random effects meta-analysis methodology. Meta-analysis of data from 8 trials (randomized n = 2,214) indicated that N-acetylcysteine significantly reduced the odds of experiencing one or more exacerbations over the treatment period (odds ratio = 0.49, 95% confidence interval [0.32-0.74], p = 0.001). Treatment effect was not reduced in studies which enrolled >50% active smokers (odds ratio = 0.36 [0.24-0.55], p < 0.001), although a greater effect was observed with exclusion of subjects using concurrent inhaled corticosteroids (odds ratio = 0.42 [0.32-0.54], p < 0.0001), suggesting that inhaled steroids attenuate the effect of N-acetylcysteine. The use of N-acetylcysteine significantly reduces the odds of exacerbation in patients with COPD, an effect possibly attenuated by inhaled steroids but not smoking. This analysis suggests treatment with N-acetylcysteine may be beneficial in a subset of patients with COPD.