The quality of evidence is downgraded by study limitations (unclear allocation concealment), and by inconsistency (variability in results).
A Cochrane review [Abstract] 1 included 38 studies with a total of 10 377 subjects. Studies lasted between two months and three years and investigated a range of mucolytics, including N-acetylcysteine, carbocysteine, erdosteine, and ambroxol, given at least once daily. The likelihood of being exacerbation-free during the study period was greater in the mucolytic group (table T1). The number needed to treat (NNTB) with mucolytics for an additional beneficial outcome for an average of 10 months - to keep an additional participant free from exacerbations - was 8 (95% CI 7 to 10). However, the more recent trials show less benefit of treatment than the earlier trials included in this review. The use of mucolytics was associated with a reduction of exacerbations per participant per month compared with placebo.The number of days of disability (sick days) per month also fell (MD -0.43 days, 95% CI -0.56 to -0.30; 9 studies, n=2 259), and hospitalisations were reduced (table T1). The impact on quality of life as measured by the total St George Respiratory Questionnaire (SGRQ) score was smaller than the clinical minimally important difference of 4 units (MD -1.37, 95% CI -2.85 to 0.11; 7 studies, n=2 721), and the confidence interval includes no difference.. Mucolytic treatment was not associated with any significant increase in adverse effects or mortality (table T1).
| Outcome* | Relative effect (95% CI) | Assumed risk - Placebo | Corresponding risk - Mucolytic (95% CI) | Participants (studies) |
|---|---|---|---|---|
| *Follow-up: 2 to 36 months | ||||
| Participants with no exacerbations | OR 1.753(1.56 to 1.91), I2 =62% | 386 per 1000 | 521 per 1000(495 to 545) | 6 723(28 studies) |
| Days of disability per participant per month | - | Mean days of disability per participant per month 1.57 days | MD 0.43 days lower(0.56 lower to 0.30 lower) | 2 259(9 studies) |
| Health-related quality of life (total score SGRQ; scale from 1 to 100; lower scores indicate better quality of life) | - | Mean SGRQ total score 39.02 points | MD 1.37 lower(2.85 lower to 0.11 higher) | 2 721(7 studies) |
| Hospitalisations | OR 0.68 (0.52 to 0.89), I2 =58% | 188 per 1000 | 136 per 1000(107 to 171) | 1 833(5 studies) |
| Adverse effects | OR 0.88(0.78 to 1.00) | 235 per 1000 | 205 per 1000(185 to 224) | 7 264(24 studies) |
| Death during study period | OR 1.03(0.52 to 2.03) | 11 per 1000 | 10 per 1000(5 to 20) | 3 527(11 studies) |
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