Mucolytic agents for chronic bronchitis or chronic obstructive pulmonary disease

Mucolytics are medicines taken orally that may loosen sputum, making it easier to cough it up. Mucolytics may have other beneficial effects on lung infection and inflammation and may be useful in the treatment of people with chronic obstructive pulmonary disease (COPD) or chronic bronchitis. This review assessed how effective they were in these patients. Review authors looked at 34 studies with a total of 9367 patients. Results showed a small reduction in the number of exacerbations (worsening of disease/symptoms) experienced by the patient if the medication was taken on a regular basis - that is, approximately one less patient with an exacerbation for every eight treated with a mucolytic over 10 months. However, this review includes a mix of small older studies and large newer ones, with newer ones showing less benefit. The medicines appear to be safe and well tolerated; however we are unsure about their impact on quality of life and on risk of hospitalisation.

Authors' conclusions: 

In participants with chronic bronchitis or COPD, we are moderately confident that treatment with mucolytics may produce a small reduction in acute exacerbations and a small effect on overall quality of life. Our confidence in the results is reduced by the fact that effects on exacerbations shown in early trials were larger than those reported by more recent studies, possibly because the earlier smaller trials were at greater risk of selection or publication bias, thus benefits of treatment may not be as great as was suggested by previous evidence.

Read the full abstract...

Individuals with chronic bronchitis or chronic obstructive pulmonary disease (COPD) may suffer recurrent exacerbations with an increase in volume or purulence of sputum, or both. Personal and healthcare costs associated with exacerbations indicate that any therapy that reduces the occurrence of exacerbations is useful. A marked difference among countries in terms of prescribing of mucolytics reflects variation in perceptions of their effectiveness.


Primary objective

• To determine whether treatment with mucolytics reduces frequency of exacerbations and/or days of disability in patients with chronic bronchitis or chronic obstructive pulmonary disease.

Secondary objectives

• To assess whether mucolytics lead to improvement in lung function or quality of life.

• To determine frequency of adverse effects associated with use of mucolytics.

Search strategy: 

We searched the Cochrane Airways Group Specialised Register and reference lists of articles on 10 separate occasions, most recently in July 2014.

Selection criteria: 

We included randomised studies that compared oral mucolytic therapy versus placebo for at least two months in adults with chronic bronchitis or COPD. We excluded studies of people with asthma and cystic fibrosis.

Data collection and analysis: 

This review analysed summary data only, most derived from published studies. For earlier versions, one review author extracted data, which were rechecked in subsequent updates. In later versions, review authors double-checked extracted data and then entered data into RevMan for analysis.

Main results: 

We added four studies for the 2014 update. The review now includes 34 trials, recruiting a total of 9367 participants. Many studies did not clearly describe allocation concealment; hence selection bias may have inflated the results, which reduces our confidence in the findings.

Results of 26 studies with 6233 participants show that the likelihood that a patient could be exacerbation-free during the study period was greater among mucolytic groups (Peto odds ratio (OR) 1.75, 95% confidence interval (CI) 1.57 to 1.94). However, more recent studies show less benefit of treatment than was reported in earlier studies in this review. The overall number needed to treat with mucolytics for an additional beneficial outcome for an average of 10 months - to keep an additional participant free from exacerbations - was eight (NNTB 8, 95% CI 7 to 10). Use of mucolytics was associated with a reduction of 0.03 exacerbations per participant per month (mean difference (MD) -0.03, 95% CI -0.04 to -0.03; participants = 7164; studies = 28; I2 = 85%) compared with placebo, that is, about 0.36 per year, or one exacerbation every three years. Very high heterogeneity was noted for this outcome, so results need to be interpreted with caution. The type or dose of mucolytic did not seem to alter the effect size, nor did the severity of COPD, including exacerbation history. Longer studies showed smaller effects of mucolytics than were reported in shorter studies.

Mucolytic use was associated with a reduction of 0.43 days of disability per participant per month compared with placebo (95% CI -0.56 to -0.30; studies = 13; I2 = 61%). With mucolytics, the number of people with one or more hospitalisations was reduced, but study results were not consistent (Peto OR 0.68, 95% CI 0.52 to 0.89; participants = 1788; studies = 4; I2 = 58%). Investigators reported improved quality of life with mucolytics (MD -2.64, 95% CI -5.21 to -0.08; participants = 2231; studies = 5; I2 = 51%). Although this mean difference did not reach the minimal clinically important difference of -4 units, we cannot assess the population impact, as we do not have the data needed to carry out a responder analysis. Mucolytic treatment was not associated with any significant increase in the total number of adverse effects, including mortality (Peto OR 1.03, 95% CI 0.52 to 2.03; participants = 2931; studies = 8; I2 = 0%), but the confidence interval is too wide to confirm that the treatment has no effect on mortality.