Mucus is largely composed of glycoproteins. These are large molecules containing several disulfide bridges. Mucolytic agents are sulfur compounds (acetylcysteine) such as N-acetylcysteine that break up the disulfide bridges making the molecules smaller and the mucus more viscous. They act mainly when applied directly by inhalation or during bronchoscopy. Their effectiveness when used orally is doubtful.
Completely different from sulfur compounds is DNase (not shown), which cleaves long DNA molecules. In cystic fibrosis (CF), inflammatory cells are abundant in the airway lumen and their DNA is released after degradation. The long molecules make the mucus very sticky. DNase is often very effective in CF making the sputum watery within a short time. DNase is not beneficial to all CF patients however.
DNAse and N-acetylcysteine work best when inhaled.
Extra info: These enzymes should be inhaled for best exposure at their site of action. If given orally, these agents would be degraded in the GI tract.
Mucolytic agents decrease mucus production.
Extra info: These agents break down the disulfide bonds, making the mucus more viscous. This action does not decrease the amount of mucus produced.
Mucolytic agents improve mucociliary clearance.
Extra info: By making the mucus more viscous, the host's mucociliary process is more efficient at clearing the mucus.