General characteristics and mechanism of action
Adsorbents are a class of substances whose therapeutic effect is driven not by chemical reactions, but by physicochemical properties. Their mechanism of action is based on three main processes:
- Surface coating. The drugs are evenly distributed, covering the skin or mucous membranes.
- Absorption (adsorption). Across their extensive surface, powdered substances bind and retain various chemical compounds.
- Protective function. By coating and absorbing aggressive substances, the drugs reliably protect sensitive nerve endings from any irritation.
For a substance to be used in medical practice as an adsorbent, it must strictly meet several physicochemical requirements. First, it must be completely insoluble in water. Second, it must have no intrinsic irritating effect on tissues. Third, the drug must be chemically inert—it must not enter into chemical interactions with other substances or body tissues.
Agents for external use: Talc
A classic representative of adsorbents for external use is talc (Talcum). Chemically, it is magnesium silicate, with the formula $4SiO_2 \cdot 3MgO \cdot H_2O$.
The localization of talc's action is limited to the skin. When applied to the skin, it exerts the following pharmacological effects:
- Actively adsorbs secretions produced by sweat and sebaceous glands.
- Creates a barrier that protects the skin from mechanical irritation (friction).
- Exhibits a pronounced drying effect.
Due to its drying and protective properties, talc is very often used in dermatology, where it acts as an important component of various therapeutic pastes.
Agents for internal use: Activated charcoal
For internal use, activated charcoal (Carbo activatus) is used. This drug is of plant or animal origin. The main feature of its production is special processing, including extremely fine grinding. This exact process allows for a multiple-fold increase in the drug's adsorption surface.
Activated charcoal is taken internally strictly as an aqueous suspension. The mechanism of action and indications for prescription depend on the clinical situation:
- Acute poisoning. The drug is effective in intoxication with alkaloids, heavy metal salts, and foodborne toxic infections. Entering the gastrointestinal tract, charcoal actively adsorbs toxins on its surface, preventing their further absorption through the intestinal mucosa into the systemic bloodstream.
- Flatulence. In case of excessive gas accumulation in the intestinal lumen, charcoal binds (adsorbs) them, reducing pressure and eliminating discomfort.
To remember the requirements for adsorbents, recall the "rule of three NOs": NO dissolution (in water), NO irritation (of tissues), NO reaction (chemically inert).
Class and exam questions
Why are adsorbents always produced in the form of powders?
Fine grinding is necessary to create the largest possible adsorption surface. The smaller the particles, the more toxins or secretions the drug can absorb.
How does activated charcoal help in foodborne toxic infections?
Taken as an aqueous suspension, charcoal coats the gastrointestinal mucosa and adsorbs toxins on its surface, physically preventing them from being absorbed into the blood.
What is the chemical formula of talc and where is it used?
Talc is magnesium silicate. It is used exclusively externally on the skin, including as part of drying pastes.
What else to study on this topic
- Specifics of preparing an aqueous suspension of activated charcoal
- Mechanism of protecting sensitive nerve endings of mucous membranes
- The role of magnesium silicate in protecting the skin from mechanical irritation
- Specifics of binding alkaloids and heavy metal salts in the gastrointestinal tract
- Use of adsorbents in the combination therapy of flatulence
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