The effect of oral N-acetylcysteine in chronic bronchitis: a quantitative systematic review

The role of N-acetylcysteine (NAC) in the treatment of chronic bronchitis i s unclear, Since a number of studies have been published on this topic, a s ystematic review of published studies seems justified. A systematic search (Medline, Embase, Cochrane Library, bibliographies, no language restriction) for published randomized trials comparing oral NAC wi th placebo in patients with chronic bronchitis was performed, Dichotomous d ata on prevention of exacerbation, improvement of symptoms and adverse effe cts were extracted from original reports, The relative benefit and number-n eeded-to-treat were calculated for both individual trials and combined data . Thirty-nine trials were retrieved; eleven (2,011 analysed patients), publis hed 1976-1994, were regarded as relevant and valid according to preset crit eria. In nine studies, 351 of 723 (48.5%) patients receiving NAC had no exa cerbation compared with 229 of 733 (31.2%) patients receiving placebo (rela tive benefit 1.56 (95% confidence interval (CI) 1.37-1.77), number-needed-t o-treat 5.8 (95% CI 4.5-8.1), There was no evidence of any effect of study period (12-24 weeks) or cumulative dose of NAC on efficacy. In five trials, 286 of 466 (61.4%) patients receiving NAC reported improvement of their sy mptoms compared with 160 of 462 (34.6%) patients receiving placebo (relativ e benefit 1.78 (95% CI 1.54-2.05), number-needed-to-treat 3.7 (95% CI 3.0-4 .9)). With NAC, 68 of 666 (10.2%) patients reported gastrointestinal advers e effects compared with 73 of 671 (10.9%) taking placebo. With NAC, 79 of 1 ,207 (6.5%) patients withdrew from the study due to adverse effects, compar ed with 87 of 1,234 (7.1%) receiving placebo. In conclusion, with treatment periods of similar to 12-24 weeks, oral N-ace tylcysteine reduces the risk of exacerbations and improves symptoms in pati ents with chronic bronchitis compared with placebo, without increasing the risk of adverse effects, Whether this benefit is sufficient to justify the routine and long-term use of N-acetylcysteine in all patients with chronic bronchitis should be addressed in further studies and cost-effectiveness an alyses.