In general, clearance ability is hampered by bonding to surfaces (stickiness) and by the viscosity of mucous secretions in the lungs. In turn, the viscosity is dependent upon the concentration of mucoprotein in the secretions.
Expectorants and mucolytic agents are different types of medication, yet both are intended to promote drainage of mucus from the lungs.
An expectorant (from the Latin expectorare, to expel or banish) works by signaling the body to increase the amount or hydration of secretions, resulting in more yet clearer secretions and as a byproduct lubricating the irritated respiratory tract. One expectorant, guaifenesin, is commonly available in many cough syrups. Often the term “expectorant” is incorrectly extended to any cough medicine, since it is a universal component.
A mucolytic agent is an agent which dissolves thick mucus and is usually used to help relieve respiratory difficulties. It does so by dissolving various chemical bonds within secretions, which in turn can lower the viscosity by altering the mucin-containing components.
Any of these effects could improve airway clearance during coughing.
An expectorant increases bronchial secretions and mucolytics help loosen thick bronchial secretions. Expectorants reduce the thickness or viscosity of bronchial secretions thus increasing mucus flow that can be removed more easily through coughing. Mucolytics break down the chemical structure of mucus molecules. The mucus becomes thinner and can be removed more easily through coughing.— Adams, Holland, & Bostwick, 2008, p. 591
- Adams, Michael; Holland, Leland Norman; Bostwick, Paula Manuel (2016). Pharmacology for Nurses: A Pathophysiologic Approach (5 ed.). Pearson Education. p. 960. ISBN 978-0134255163.
- Rubin, Bruce K (1 July 2007). “Mucolytics, Expectorants, and Mucokinetic Medications”. Respiratory Care. 52 (7).
2. https://www.ncbi.nlm.nih.gov/books/NBK57832/ Nation Center for Biotechnology Information