Mechanisms of action and local effects
The action of heavy metal salts varies depending on their concentration:
- Low concentrations (antimicrobial effect): metal ions bind to sulfhydryl groups of bacterial enzymes. This leads to the blockade of vital processes and the death of the microbial cell.
- High concentrations (tissue effect): metals react with macroorganism proteins, causing their denaturation and the formation of specific compounds known as albuminates.
Depending on the properties of a specific metal, its solubility, and degree of dissociation, local effects are divided into three levels based on the depth of tissue damage:
- Astringent action: partial denaturation occurs only in the most superficial layers. A protective film (coagulum) is formed, tissue becomes denser, its permeability decreases, and inflammation subsides.
- Irritant action: the substance penetrates deeper, affecting living cells and nerve endings.
- Caustic action: harsh exposure with denaturation of a large mass of proteins, leading to tissue necrosis.
Mercury and silver preparations
Mercury (Hg) has the strongest effect in the heavy metal series. Preparations are classified by solubility:
- Soluble: mercury(II) chloride (corrosive sublimate). Easily dissociates in water, exhibits potent antimicrobial and irritant effects. Due to extremely high toxicity and the ability to absorb through the skin, it is used exclusively for disinfecting utensils and linens.
- Insoluble: mercury amidochloride and yellow mercuric oxide. Less toxic, used as ointments for treating pyoderma and eye infections (conjunctivitis, keratitis).
Silver (Ag) is primarily represented by silver nitrate (lunar caustic). At concentrations up to 2%, it acts as an astringent, and above 5% as a caustic (for removing warts and excessive granulations). The antimicrobial effect of silver is biphasic:
- Bactericidal phase: rapid microbial death due to the precipitation of their proteins by silver ions.
- Bacteriostatic phase: silver nitrate forms an albuminate in tissues, from which metallic silver is gradually released, persistently blocking bacterial enzymes.
There are also organic non-dissociating preparations (silver proteinate, colloidal silver), but today they are rarely used, having given way to modern antibiotics.
Bismuth, copper, and zinc preparations
Bismuth (Bi) is widely used due to its astringent, drying, and anti-inflammatory properties. The mechanism is based on the coagulation of exudate and mucous proteins with the formation of a protective film.
- Bismuth subgallate (dermatol) is used in dermatology for weeping ulcers and eczema, in proctology for hemorrhoids, and in gastroenterology for diarrhea and ulcerative colitis.
- Bismuth tribromophenate (xeroform) additionally possesses a weak antiseptic effect and is an essential component of the famous Vishnevsky ointment.
Copper (Cu) and Zinc (Zn) are represented by sulfates. In solution form, they exert antiseptic and astringent effects. They are prescribed for inflammatory processes of mucous membranes in ophthalmology, ENT practice, urology, and gynecology.
Briefly: answers to topical questions
What symptoms and signs are characteristic of acute heavy metal salt poisoning, and what is the first aid?
Specific clinical symptoms of acute heavy metal salt poisoning are not described in the provided materials. Necrotic nephrosis is mentioned, for example, in mercury(II) chloride poisoning.
The following are indicated as agents used in heavy metal poisoning:
- Tannin — forms poorly soluble compounds with toxins, preventing their absorption.
- Demulcents (enveloping agents) — coat the GI mucosa with a colloidal film, are capable of enveloping toxic substances, slowing their absorption, and promoting excretion.
- Penicillamine — used as an antidote in heavy metal poisoning.
- Sodium thiosulfate — in heavy metal poisoning, including mercury and lead, enters into a chemical reaction to form non-toxic compounds.
What lead preparations are used in medical practice, and what is their pharmacological effect?
Lead acetate is indicated among lead preparations in the provided materials.
Pharmacological effect: classified as an astringent. For lead, it is also noted that it is the weakest in the activity series in terms of antimicrobial and local action strength among the listed heavy metal salts.
Application of lead acetate: for skin lesions and wounds in the form of lotions and rinses.
Metal activity rule: Mercury, Silver, Copper, Zinc, Bismuth, Lead (from strongest to weakest).
Class and exam questions
Why are heavy metal salts unsuitable for disinfecting pus or blood?
Biological secretions contain a high amount of protein. Metal ions instantly bind to these proteins, forming albuminates, and fail to reach microorganisms, causing antimicrobial activity to drop sharply.
What is the fundamental difference between astringent and caustic action?
Astringent action affects only the most superficial layers of tissues, forming a thin protective film of coagulated proteins. Caustic action penetrates deeply, causing harsh denaturation of a large volume of tissues and their necrosis.
How exactly does silver nitrate provide a prolonged antimicrobial effect?
Following the initial rapid destruction of bacteria, silver nitrate binds to tissues, forming silver albuminate. Metallic silver is slowly and gradually restored from this compound, continuing to block microbial enzymes.
What else to study on this topic
- Toxicology of soluble mercury preparations and the pathogenesis of poisoning
- Detailed analysis of the biphasic mechanism of action of silver nitrate
- Pharmacodynamics of bismuth preparations in gastroenterology and proctology
- Comparative characteristics of organic and inorganic silver compounds
- Features of the use of copper and zinc sulfates in ophthalmology
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