Abstract
It has been shown that mucus hypersecretion is associated with greater susceptibility for chronic obstructive pulmonary disease (COPD), excess forced expiratory volume in 1 s decline, hospitalisations and excess mortality. The effects of mucoactive drugs on outcomes have been reviewed in several meta-analyses, the largest one including 26 studies. 21 studies were performed in patients with chronic bronchitis and five in patients with COPD. The majority of these trials were performed with N-acetylcysteine (n = 13) and carbocysteine (n = 3). Overall, there was a significant reduction in exacerbations (0.05 per patient per month) and the number of days with disability (0.56 days per patient per month). Mucolytics were well tolerated and the number of adverse events was lower than with placebo (odds ratio 0.78). In the largest and best designed study with N-acetylcysteine in 523 patients with COPD, the reduction in exacerbations was only observed in patients not taking inhaled corticosteroids. In addition, a 374 mL reduction in functional residual capacity was found. A recent large study (n = 709) with high-dose carbocysteine (1,500 mg·day⁻¹) demonstrated a significant effect on exacerbations (25% reduction) and also reported an improvement in health-related quality of life (-4.06 units in St George's Respiratory Questionnaire). It is unclear what the mechanisms underlying these effects may be and which phenotypes benefit from this treatment. On the basis of this evidence mucoactive drugs may deserve consideration in the long-term treatment of COPD.