At least 50 percent of all smokers develop chronic bronchitis, and up to 15 percent become incapacitated because of chronic obstructive pulmonary disease (COPD). The mainstay of treatment during exacerbations is antibiotic or steroid therapy, but other agents are needed to reduce the frequency and severity of exacerbations. In some European countries, mucolytic agents (such as bromhexine or iodinated glycerol) are widely used to treat chronic bronchitis. Poole and Black conducted a meta-analysis to determine the potential benefits of mucolytic therapy.

The authors used the Cochrane Airways Group Register to search for studies of mucolytic therapy for chronic bronchitis or COPD. Four of the 27 double-blind, placebo-controlled studies they identified were excluded because they lacked information on the primary outcome. Two of the remaining studies focused on COPD, and 21 studied chronic bronchitis. The studies involved more than 2,000 patients treated with mucolytics and 2,000 patients given placebo.

Regular use of mucolytics was associated with small, nonsignificant changes in measures of pulmonary function but with significant reductions of about one-half day per month in days of illness. The chance of being free of exacerbations was approximately doubled. The calculated number to treat for one patient to remain free of exacerbations was six. Adverse effects were noted and occurred with the same frequency in treated and placebo groups.

The authors conclude that regular use of mucolytic agents modestly reduces exacerbations and the number of days of illness in patients with chronic bronchitis and COPD. The benefits may be greatest in patients with more advanced disease, but the cost-effectiveness of mucolytic therapy has not been established.