Mechanisms of Action: How Drugs Reach the Bronchi
Expectorants are divided into two major groups based on how they stimulate bronchial gland activity.
- Reflex-acting agents. These trigger the gastropulmonary reflex. When a patient takes the drug per os, the active substances moderately irritate the gastric mucosal receptors. The signal travels to the medulla oblongata, stimulates vagus nerve centers, and returns to the bronchi. Result: the glands secrete more liquid fluid, sputum viscosity and adhesiveness drop, and the ciliated epithelium and bronchiolar smooth muscle actively push contents upward.
- Direct (resorptive) acting agents. These drugs are absorbed into the systemic circulation and excreted directly by the respiratory mucosa. As they pass through the bronchi, they stimulate glandular secretion and increase ciliary motility.
Herbal Reflex-Acting Agents
Nature has provided medicine with numerous herbs rich in alkaloids, saponins, and essential oils that effectively clear the respiratory tract.
- Thermopsis herb (Herba Thermopsidis). Contains alkaloids (cytisine, methylcytisine, pachycarpine, thermopsine). Acts in a strictly dose-dependent manner: weak infusions (1:300) provide an excellent expectorant effect, whereas concentrated ones (1:10) excite the vomiting center.
- Licorice root (Radices Glycyrrhizae). Acts comprehensively. Glycyrrhizic acid reduces inflammation, while flavonoids (liquiritin) relax smooth muscle, providing a spasmodic effect. Included in pectoral elixir (Elixir pectorale).
- Marshmallow root (Radices Althaeae). Contains polysaccharides, acting as an expectorant and anti-inflammatory agent. Used as the basis for the popular drug Mucaltin, pectoral herbal teas (species pectoralis), and children's dry mixtures.
- Senega root (Radices Polygalae) and ipecac root. Used as decoctions due to their high saponin content.
A special group consists of essential oil-bearing plants. They work on two fronts: first reflexively from the stomach, and then directly when the absorbed essential oils are excreted via the respiratory tract, further thinning the sputum.
Synthetic and Combination Drugs
Pharmacology actively utilizes combinations of plant extracts with saline and synthetic components to enhance therapeutic efficacy.
- Cough tablets (Tabulettae contra tussim). A simple yet effective combination: Thermopsis powder plus sodium bicarbonate.
- Pertussin (Pertussin). A syrup based on thyme (or caraway) extract with added potassium bromide.
- Dry cough mixture for adults (Mixtura sicca contra tussim pro adultis). A complex formulation dissolved in water prior to administration. Includes dry extracts of Thermopsis and licorice, anise oil, ammonium chloride, sodium benzoate, sodium bicarbonate, and sugar.
Among purely synthetic reflex agents, terpin hydrate stands out. It is frequently prescribed for chronic bronchitis, though it is strictly contraindicated in patients with high gastric acidity due to the risk of exacerbating hyperacid states.
Direct-Acting Agents
This group includes salts: potassium iodide and sodium bicarbonate.
Their primary feature is the variability of administration routes. Unlike reflex agents, which must enter the stomach to trigger the reflex, direct-acting agents can be administered both orally and via inhalation. Upon reaching the bronchial mucosa (via systemic circulation or inhaled air), they effectively liquefy sputum and cause the ciliated epithelium to beat more intensely.