The airway mucosa responds to
infection and
inflammation in a variety of ways. This response often includes surface mucous (goblet) cell and submucosal gland
hyperplasia and
hypertrophy, with mucus hypersecretion. Products of
inflammation, including neutrophil-derived
deoxyribonucleic acid (
DNA) and filamentous actin (
F-actin), effete cells, bacteria, and cell debris, all contribute to mucus purulence and, when this mucus is expectorated it is called sputum. Mucoactive medications are intended to serve one of 2 purposes; either to increase the ability to expectorate sputum or to decrease mucus hypersecretion. Mucoactive medications have been classified according to their proposed mechanisms of action. Increased knowledge of the properties of mucus has given us tools to better understand the mechanisms of airway disease and mucoactive
therapy.
Expectorants are thought to increase the volume or hydration of airway secretions. Systemic hydration and classic
expectorants have not been demonstrated to be clinically effective. Modifiers of airway water transport are being clinically investigated as
expectorants.
Mucolytics degrade
polymers in secretions. The classic
mucolytics have free
thiol groups to degrade
mucin.
Peptide mucolytics break pathologic filaments of neutrophil-derived
DNA and actin in sputum. Nondestructive mucolysis includes
mucin dispersion by means of charge shielding. Mucokinetics are medications that increase mucociliary efficiency or
cough efficiency.
Cough flow can be increased by
bronchodilators in patients with airway hyperreactivity. Abhesives such as
surfactants decrease mucus attachment to the cilia and epithelium, augmenting both
cough and mucociliary clearance. Mucoregulatory agents reduce the volume of airway mucus secretion and appear to be especially effective in hypersecretory states such as bronchorrhea,
diffuse panbronchiolitis, and some forms of
asthma. Mucoregulatory agents include
anti-inflammatory agents (
indomethacin, glucocorticosteroids),
anticholinergic agents, and some
macrolide antibiotics. Classifying mucoactive agents should help us to develop and evaluate new types of
therapy and to better direct
therapy toward the patients who are most likely to benefit.