Classification of dyes by chemical structure
In pharmacology, the group of dyes is conventionally divided into three main categories depending on their chemical structure:
- Triphenylmethane derivatives. This group includes the well-known brilliant green.
- Phenothiazine derivatives. The main representative is methylthioninium chloride, better known in medical practice as methylene blue.
- Acridine derivatives. These include ethacridine lactate (rivanol).
Brilliant green (Viride nitens)
This is a highly active antiseptic that exerts a pronounced bactericidal effect on gram-positive bacteria. In addition, the drug exhibits fungicidal activity against pathogenic fungi.
Main indications for use:
- Traumatic skin injuries: treatment of fresh cuts, abrasions, as well as post-traumatic and postoperative scars.
- Pyodermas (purulent-inflammatory diseases): treatment of furunculosis and carbunculosis.
- Neonatology: standard umbilical cord care in newborns.
- Ophthalmology: treatment of blepharitis and hordeolum (stye).
The drug is available in the form of aqueous and alcoholic solutions, as well as convenient medical pencils. Brilliant green is actively used for impregnating bactericidal patches and is an active component of corn collodion and Novikov's liquid.
Methylthioninium chloride (Methylene blue)
As an antiseptic, this drug is somewhat inferior to brilliant green. Its mechanism of action is based on direct interaction with proteins and mucopolysaccharides of microorganisms. Alcoholic solutions are used topically for burns and pyodermas, while aqueous solutions are used locally and internally for irrigation in urinary bladder and urethral infections.
Toxicological properties and antidote role A unique feature of methylene blue is its ability to act as a hydrogen ion donor or acceptor in oxidation-reduction reactions. The effect strictly depends on the administered dose (administered intravenously in a glucose solution):
- Low concentrations: the drug reduces methemoglobin back to normal hemoglobin. This property is used in the treatment of methemoglobinemia caused by aniline or nitrite poisoning.
- High concentrations: the drug, conversely, oxidizes hemoglobin, converting it into methemoglobin. This is vital in cyanide (hydrocyanic acid) poisoning. The resulting methemoglobin tightly binds cyanides, forming a non-toxic complex—cyanmethemoglobin. High doses are also used for hydrogen sulfide and carbon monoxide (CO) intoxication.
Ethacridine lactate (Rivanol)
The drug is active predominantly against coccal flora, primarily streptococci. Its mechanism of action is also dose-dependent:
- In low concentrations it exhibits a certain selectivity, specifically inhibiting the activity of microbial cell enzymes.
- In high concentrations it causes total coagulation of microbial proteins.
Application in surgery and traumatology: Ethacridine lactate is widely used topically. As lotions and tampons, it is prescribed for the treatment of purulent-inflammatory lesions of soft tissues and skin (boils, carbuncles, abscesses, phlegmons, infected wounds, and ulcers). In addition, rivanol solutions are used for prophylactic and therapeutic irrigation of cavities in purulent processes: peritoneal, pleural, articular, and the urinary bladder cavity.
Briefly: answers to topical questions
What concentrations of aqueous methylene blue solutions are used for urinary bladder irrigation?
Sources for methylthioninium chloride (methylene blue) indicate topical/internal use as irrigations for urethral and bladder infections. A 0.02% concentration is given for aqueous methylthioninium chloride solution for irrigating purulent cavities.
To memorize the antidote action of methylene blue, use the "Low/High" rule: Low dose — Minuses (reduces) methemoglobin to hemoglobin. High dose — Recreates (oxidizes) methemoglobin so that it binds cyanides.
Class and exam questions
Why are dyes not recommended for application to heavily suppurating wounds?
The antimicrobial activity of all dyes is significantly reduced in the presence of organic substrates. Pus and blood inactivate the drug, making its use less effective.
Which of the dyes has antifungal action?
Fungicidal action against pathogenic fungi is characteristic of brilliant green (Viride nitens). In addition, it is a highly active bactericidal agent against gram-positive flora.
What is the essence of the antidote action of methylene blue in cyanide poisoning?
When administered in high concentrations, the drug converts hemoglobin into methemoglobin. The latter reacts with cyanides, binding them and forming a non-toxic compound—cyanmethemoglobin.
How does the concentration of ethacridine lactate affect its mechanism of action?
In low concentrations, the drug acts selectively, inhibiting the activity of microbial enzymes. When high concentrations are used, non-specific coagulation of bacterial cell proteins occurs.
What else to study on this topic
- Biochemical mechanisms of dye interaction with bacterial mucopolysaccharides.
- Redox reactions during intravenous administration of methylthioninium chloride.
- Comparative characteristics of the efficacy of dyes and halogen-containing antiseptics.
- Pharmacological composition and application of Novikov's liquid in dermatology.
- Features of serous cavity irrigation with ethacridine lactate solutions.
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