Mechanisms of action: how drugs reach the bronchi
Expectorants are divided into two major groups depending on how they stimulate the activity of bronchial glands.
- Reflex action. They trigger the gastro-pulmonary reflex. The patient takes the drug orally (per os), and the active substances moderately irritate the receptors of the gastric mucosa. The signal travels to the medulla oblongata, stimulates vagus nerve centers, and returns to the bronchi. Result: the glands secrete more fluid, sputum viscosity and adhesiveness decrease, and the ciliated epithelium and smooth muscle of the bronchioles actively push the contents upward.
- Direct (resorptive) action. The drugs are absorbed into the systemic circulation and excreted directly by the respiratory mucosa. Passing through the bronchi, they stimulate glandular secretion and increase the motility of epithelial cilia.
Herbal reflex preparations
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). Works in a strictly dose-dependent manner: weak infusions (1:300) provide an excellent expectorant effect, whereas concentrated ones (1:10) stimulate the vomiting center.
- Licorice root (Radices Glycyrrhizae). Acts comprehensively. Glycyrrhizic acid reduces inflammation, while flavonoids (liquiritin) relax smooth muscle, providing a spasmolytic effect. It is a component of pectoral elixir.
- Marshmallow root (Radices Althaeae). Contains polysaccharides, acting as an expectorant and anti-inflammatory agent. It is used to produce the popular drug Mukaltin, pectoral teas (species pectoralis), and dry pediatric mixtures.
- Senega root (Radices Polygalae) and ipecac root. Used as decoctions due to their high saponin content.
A special group comprises essential oil-bearing plants. They work on two fronts: first reflexively from the stomach, and then directly when absorbed essential oils are excreted via the respiratory tract, further thinning the sputum.
Synthetic and combined agents
Pharmacology actively utilizes combinations of herbal extracts with saline and synthetic components to enhance the therapeutic effect.
- 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 mixture for adults (Mixtura sicca contra tussim pro adultis). A complex formulation that must be dissolved in water before administration. It 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, but it is strictly contraindicated in patients with high gastric acidity due to the risk of exacerbating hyperacid conditions.
Direct-acting drugs
This group includes salts: potassium iodide and sodium bicarbonate.
Their main feature is the variability of administration routes. Unlike reflex agents, which must enter the stomach to trigger the reflex, direct-acting drugs can be administered both orally and via inhalation. Reaching the bronchial mucosa (from the systemic circulation or via inhaled air), they effectively thin the sputum and stimulate ciliary epithelial activity.
Briefly: answers to topical questions
Which herbal preparations contain saponins?
Saponins are found in preparations based on thermopsis, licorice, and senega.
- Lanceleaf thermopsis herb (Herba Thermopsidis Lanceolata) contains saponins combined with alkaloids and essential oils.
- Licorice roots (Radices Glycyrrhizae) contain glycyrrhizic acid, which is a triterpene saponin providing an anti-inflammatory effect.
- Senega preparations (radices Polygalae) feature saponins as the active substance, used as a decoction for expectorant effects.
What are the main indications for expectorant use?
According to guidelines, the main indications for expectorants are:
- Cough — expectorants and antitussives are prescribed for cough.
- Acute bronchitis and tracheitis caused by respiratory viruses, accompanied by productive cough and signs of bronchial obstruction — mucolytics and expectorants are recommended to liquefy and improve sputum clearance.
- Chronic bronchitis — an indication for terpin hydrate as an expectorant.
- Respiratory tract diseases — marshmallow preparations are used for respiratory diseases; ambroxol is used for acute and chronic respiratory conditions, including bronchitis, pneumonia, bronchial asthma, and bronchiectasis.
To understand the gastro-pulmonary reflex: "The stomach is irritated — the bronchi are cleared." Reflex-acting drugs transit via the vagus nerve, beginning their journey with an effect on the gastric mucosa.
Class and exam questions
Why does nausea occur with an overdose of expectorant herbs?
Herbal reflex-acting drugs (e.g., thermopsis herb) irritate gastric receptors. In low doses, this stimulates the bronchi, while in high doses, it strongly excites the vomiting center in the medulla oblongata.
How do essential oils affect sputum?
They possess a dual action. First, they reflexively irritate the stomach, and then they are absorbed into the blood and excreted through the respiratory tract, directly thinning the bronchial gland secretions.
Can terpin hydrate be prescribed to patients with gastritis?
The drug is contraindicated in hyperacid conditions (high acidity) because it exerts a direct irritant effect on the gastric mucosa.
What else to study on this topic
- Pharmacodynamics of individual thermopsis herb alkaloids (cytisine, pachycarpine)
- Mechanism of the anti-inflammatory action of glycyrrhizic acid
- Composition and preparation rules for pectoral teas (species pectoralis)
- Differences in the composition of dry cough mixtures for children and adults
- Features of inhalation administration of direct-acting drugs
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