Mechanisms of Action and Local Effects
The effects of heavy metal salts vary depending on their concentration:
- Low concentrations (antimicrobial effect): metal ions bind to sulfhydryl groups of bacterial enzymes. This leads to the blockade of vital metabolic processes and microbial cell death.
- High concentrations (tissue effects): metals react with host proteins, causing their denaturation and the formation of specific compounds called albuminates.
Depending on the specific metal's properties, solubility, and degree of dissociation, local effects are categorized into three levels based on the depth of tissue damage:
- Astringent action: partial denaturation occurs only in the superficial layers. A protective coagulated film forms, tissue density increases, permeability decreases, and inflammation subsides.
- Irritant action: the substance penetrates deeper, affecting viable cells and nerve endings.
- Caustic action: harsh exposure resulting in the denaturation of a large mass of proteins, leading to tissue necrosis.
Mercury and Silver Preparations
Mercury (Hg) exhibits the strongest activity in the heavy metal series. Preparations are categorized by solubility:
- Soluble: mercuric chloride (corrosive sublimate). It readily dissociates in water, exhibiting powerful antimicrobial and irritant effects. Due to extreme toxicity and transdermal absorption, it is used exclusively for disinfecting inanimate objects and linens.
- Insoluble: ammoniated mercury and yellow mercuric oxide. Less toxic, used as ointments for pyoderma and ocular infections (conjunctivitis, keratitis).
Silver (Ag) is primarily represented by silver nitrate (lunar caustic). At concentrations up to 2%, it acts as an astringent, while concentrations above 5% act as a caustic (for removing warts and exuberant 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 albuminates in tissues, from which metallic silver is gradually released, persistently blocking bacterial enzymes.
Organic non-dissociating preparations (silver proteinate, colloidal silver) also exist, but are rarely used today, having been largely superseded by modern antibiotics.
Bismuth, Copper, and Zinc Preparations
Bismuth (Bi) is widely used due to its astringent, drying, and anti-inflammatory properties. The mechanism relies on the coagulation of exudate and mucous proteins to form 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 mild antiseptic activity and is a mandatory component of Vishnevsky ointment.
Copper (Cu) and Zinc (Zn) are represented by their 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.