Mucus-controlling agents: past and present.

Airway mucus is the secretory product of the mucous cells. The mucus is a variable mixture of water, mucous glycoproteins, low molecular weight ions, proteins, and lipids, the physical properties of which are important for airway defense. The factors that contribute to the physical properties of mucus are complex, and there are several pharmacologic strategies that potentially can serve to improve the clearability of airway mucus. In vitro results suggest potential benefit from the additive effects of selected combinations of mucoactive medications. Further studies are required to confirm these findings, to perform direct assessments of mucus clearability, and to extend the observations to patients with various types of pulmonary diseases for which mucoactive treatments are required.