Mucoactive Agents for Productive Cough: What are The Choices?

Mucoactive agents are medicines/agents that affect mucus properties and promote secretion clearance. These agents are useful in productive cough where hypersecretion of mucus is predominant, but practically not useful at all in dry cough. There are several subgroups of mucoactive agents. Four of them are listed and described below. Note that one agent may have been classified more than in one subgroup. The important mucoactive is mucokinetic medicines and mucolytic medicines.

 

1. Expectorants / Mucokinetic
Examples: Hypertonic saline, guaifenesin, ambroxol
These medications increase secretion volume and hydrations on the respiratory tract, so that thick mucus is surrounded by more of waters, thus easier to be excreted.
Ambroxol has a little different mechanism of action. Besides promoting mucus clearance, it also possesses antioxidant and anti-inflammatory effect and a local anesthetic effect when formulated as a lozenge.
Suitable for: mild productive cough; sputum can be excreted easily/moderately easy, mild-moderate acute respiratory tract infection.
Not suitable for: massive productive cough, difficult excretion of mucus, prolonged cough due to smoking, emphysema, bronchitis.

2. Mucolytics
Examples: N-acetylcysteine, erdosteine, carbocysteine
These medications severs disulfide bonds that link mucin oligomers, thus destroying mucus structure; makes it easier to be excreted. Other effects are antioxidant and anti-inflammation.
N-acetylcysteine also possesses wide safety margin, with range of doses from 600 to about 3200-4800 mg/day. N-acetylcysteine itself is an antidote of paracetamol.
Suitable for: Massive productive cough, difficult excretion of mucus, coughs in cystic fibrosis or mucovicidosis.
Not suitable for: Patients with overt gastrointestinal complaints, especially gastric complaints.

3. Respiratory Adhesive Lubricants
Example: Ambroxol
Main key of this subclass is surfactant production. Surfactant is an "antiglue" factor in alveoli and bronchi, with function of preventing secretions from sticking to the walls of respiratory tract. Adequate surfactant production is necessary for mucus transport.
Sometimes ambroxol is considered as a respiratory adhesive lubricant, due to its effect as surfactant stimulator; even though many scientists classify ambroxol as an expectorant. But this effect is only observed in animal study and small-scale study only, so far.

4. Cough clearance agent
Based on statement of Rubin (2007), bronchodilators (beta-agonists and methylxanthine) could be classified as cough clearance agent; due to their effects on ciliary beat frequency. But due to their minimal effect on mucociliary clearance, these medicines are often classified just as bronchodilators, with predominant effect of bronchodilatation.
Suitable for: cough with history of obstructive respiratory diseases, or with dyspnea (difficulty to breath).
Not suitable for: simple productive cough. 

Comments are welcome!

References:
Malerba M & Ragnoli B. Expert Opin Drug Metab Toxicol 2008; 4(8): 1119-1129.
Rubin BK. Respir Care 2007; 52(7): 859–865.