Astringents

Mechanism of action and pharmacologic effects

The primary reaction when using astringents is 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 isolation, the following pharmacological effects develop:

• Analgesic: a direct consequence of protecting nerve endings from external irritants.
• Anti-inflammatory: the drugs cause local vasoconstriction, reduce vascular wall permeability, decrease exudate production, and generally inhibit the inflammatory response.

The drugs are usually well tolerated, but the effect is short-term and reversible. In rare cases (especially with prolonged use of metal-containing agents or individual intolerance), nausea, vomiting, and dyspepsia are possible.

Classification of astringents

Drugs are classified into two main groups depending on their origin.

1. Organic (plant-derived) They act more mildly and are used mainly in the form of decoctions, infusions, and enemas. These include preparations containing tannin. Sources include:

• Herbs: St. John's wort.
• Leaves: sage.
• Flowers: chamomile.
• Rhizomes: bistort, great burnet, cinquefoil.
• Berries: blueberry, bird cherry.
• Bark: oak.

2. Inorganic (dilute solutions of metal salts) This group includes bismuth subnitrate, dermatol (bismuth subgallate), xeroform (bismuth tribromophenate basic), lead acetate, alums, as well as zinc and copper sulfates. An important feature of metal salts is the presence of antiseptic (antimicrobial) action, which is achieved through the coagulation of proteins of the microbial cell itself.

Dose-dependent effect: in low doses, inorganic salts act as astringents, whereas in high doses, they exhibit a caustic effect (silver, aluminum, zinc, and copper salts). This property is used to remove excess granulations and stop bleeding in shallow cuts.

Clinical application

Astringents are prescribed topically and orally (enterally) for various pathologies:

• Gastrointestinal diseases: in acute inflammation, gastritis, enteritis, and colitis, plant-based remedies are used (along with antibiotics if of infectious origin). In peptic ulcer disease, chronic gastritis, and duodenitis, both plant preparations and bismuth subnitrate (a component of the combination drugs Vikair and Vikalin) are used.
• Dentistry and ENT practice: in acute and chronic gingivitis, stomatitis, and pharyngitis, plant-based remedies are preferred for rinsing.
• Dermatology and surgery: bismuth preparations in the form of ointments and powders are used to treat burns, ulcers, eczema, and dermatitis. Lotions with lead acetate and alum are applied to wounds.
• Ophthalmology and urology: irrigations and eye drops with zinc sulfate are used for urethritis, vaginitis, and conjunctivitis.

Characteristics of tannin

By chemical nature, tannin is gallotannic acid. It is obtained from gall nuts (Gallae turcicae — growths on the shoots of the Asia Minor oak) and certain plants of the Anacardiaceae family.

Application of tannin:

1. Topical: 1–2% solutions for rinsing the oral cavity and throat, 3–10% solutions and ointments for burns and ulcers.
2. Enteral (for diarrhea): pure tannin is not prescribed orally due to severe gastric irritation. Its protein compounds (Tannalbin, Tealbin) are used instead, as they do not precipitate on the gastric mucosa, ensuring action directly in the intestine.
3. Toxicological: tannin is an important antidote. A 0.5% aqueous solution is used for gastric lavage in oral poisonings by heavy metal salts and alkaloids (morphine, cocaine, atropine, nicotine). It binds toxins, preventing their absorption.

Class and exam questions

What else to study on this topic

• Mechanisms of caustic and antiseptic action of inorganic salts
• Pharmacological properties of bismuth preparations and their place in the treatment of peptic ulcer disease
• Specifics of using astringents in dental practice
• Physicochemical features of tannin interaction with alkaloids
• Principles of combining organic astringents with antibiotics

Other topics in the "Analgesics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.