Mechanism of Action and Pharmacological Effects
The primary reaction when using astringents is the partial denaturation (coagulation) of mucus or exudate proteins on the wound surface. The coagulated proteins form a dense film that isolates the underlying tissues.
Due to this insulation, the following pharmacological effects develop:
- Analgesic: A direct consequence of protecting nerve endings from external irritants.
- Anti-inflammatory: Drugs cause local vasoconstriction, reduce vascular wall permeability, decrease exudate production, and overall inhibit the inflammatory response.
The drugs are generally well tolerated, but the effect is short-lived and reversible. In rare cases (especially with prolonged use of metal-containing agents or individual intolerance), nausea, vomiting, and dyspepsia may occur.
Classification of Astringent Agents
Drugs are classified into two main groups based on their origin.
1. Organic (Herbal Origin) They act more mildly, used predominantly in the form of decoctions, infusions, and enemas. They include tannin-containing preparations. Sources include:
- Herbs: St. John's wort (Hypericum).
- Leaves: Sage (Salvia).
- Flowers: Chamomile (Matricaria).
- Rhizomes: Bistort (Bistorta), burnet (Sanguisorba), cinquefoil (Potentilla).
- Berries: Blueberry (Vaccinium myrtillus), bird cherry (Prunus padus).
- Bark: Oak (Quercus).
2. Inorganic (Weak Metal Salt Solutions) This group includes bismuth subnitrate, dermatol (bismuth subgallate), xeroform (bismuth tribromophenate basic), lead acetate, alum, as well as zinc and copper sulfates. An important feature of metal salts is their antiseptic (antimicrobial) action, achieved through the coagulation of the microbial cell's own proteins.
Concentration-dependent effects: In low doses, inorganic salts act as astringents, whereas in high doses, they exhibit a caustic (cauterizing) action (salts of silver, aluminum, zinc, copper). This property is used to remove excess granulation tissue and stop bleeding in shallow cuts.
Clinical Application
Astringents are prescribed topically and internally (enterally) for various pathologies:
- Gastrointestinal disorders: For acute inflammation, gastritis, enteritis, and colitis, herbal remedies are used (combined with antibiotics if of infectious origin). For peptic ulcer disease, chronic gastritis, and duodenitis, both herbal preparations and bismuth subnitrate are used.
- Dentistry and ENT practice: For acute and chronic gingivitis, stomatitis, and pharyngitis, herbal rinses are preferred.
- Dermatology and surgery: Bismuth preparations in the form of ointments and powders are used to treat burns, ulcers, eczema, and dermatitis. Lead acetate and alum lotions are applied to wounds.
- Ophthalmology and urology: Zinc sulfate washes and eye drops are used for urethritis, vaginitis, and conjunctivitis.
Characteristics of Tannin
Chemically, tannin is gallotannic acid. It is obtained from gall nuts (Gallae turcicae — growths on shoots of the Lesser Asian oak) and certain plants of the Anacardiaceae family.
Application of Tannin:
- Topical: 1–2% solutions for rinsing the mouth and throat; 3–10% solutions and ointments for burns and ulcers.
- Enteral (for diarrhea): Pure tannin is not administered orally due to severe gastric irritation. Its protein compounds (e.g., albuminate of tannin) are used, which do not precipitate on the gastric mucosa, ensuring action directly in the intestine.
- Toxicological: Tannin is an important antidote. A 0.5% aqueous solution is used for gastric lavage in oral poisonings with heavy metal salts and alkaloids (morphine, cocaine, atropine, nicotine). It binds toxins, preventing their absorption.