Mechanism of Action and Classification
The antimicrobial action of these compounds (from Latin detergere — to clean, wipe off) is not limited to simply washing away bacteria. It is based on three deep physicochemical processes:
- Protein Denaturation: structural changes in protein molecules inside the microbial cell, leading to the loss of their functions.
- Disruption of Substance Transport: a sharp decrease in surface tension at the phase boundary blocks the transfer of vital ions and nutrient substrates across the microbial membrane.
- Enzyme Inhibition: direct suppression of the activity of key enzyme systems of the microorganism, without which its vital activity is impossible.
In pharmacology, all detergents are divided into two large groups:
- Anionic (a classic example is green soap).
- Cationic (include quaternary ammonium compounds). This group is of the greatest interest to medicine because it possesses a much more powerful antiseptic potential.
Pharmacology of Cationic Detergents
Cationic detergents work at the cellular level: they bind tightly to the lipoproteins of bacterial membranes. This interaction destroys the barrier function of the envelope, which inevitably leads to the death of the pathogen.
Spectrum of Antimicrobial Activity:
- Bactericidal action: the drugs effectively destroy Gram-positive (G+) bacteria; however, their effect on Gram-negative (G-) flora is rather weak.
- Static action: they stop the growth and reproduction of fungi (fungistatic effect) and bacterial spores (sporostatic effect).
Factors Reducing Efficacy: It is important for a clinician to remember that the antiseptic potency of cationic detergents drops sharply under adverse conditions. These include:
- The presence of organic substrates (abundant pus, blood in the wound).
- The presence of metal ions (calcium, magnesium, iron, aluminum).
- Combined use with anionic soaps (direct chemical antagonism occurs).
Main Areas of Application:
- Strict antisepsis of the surgeon's hands and preparation of the operational field.
- Thorough treatment of wound and burn surfaces.
- Disinfection of surgical instruments, complex medical equipment, and patient care items.
Characteristics of Main Drugs
- Benzalkonium chloride (Rookal): a cationic detergent with antibacterial, antiprotozoal, and spermicidal action. The latter effect is due to damage to the sperm membrane, making fertilization impossible (used in gynecology as local contraception in the form of creams, tablets, and suppositories). It is also used externally to treat wounds, trophic ulcers, and to rinse cavities (urethra, urinary bladder). Safety issue: in a number of countries, the drug is not recommended as an antiseptic. Outbreaks of hospital-acquired infections have been registered because Pseudomonas aeruginosa and other Gram-negative bacteria are able to survive and multiply directly in its solutions.
- Miramistin: a popular cationic detergent that increases the permeability of the cytoplasmic membrane to the point of cytolysis. It features an exceptionally wide spectrum: it kills bacteria, fungi, viruses, and protozoa. An important additional effect is the stimulation of tissue regeneration. It is used for the treatment and prevention of purulent-inflammatory processes in surgery, traumatology, combustiology, urology, dermatology, dentistry, and ENT practice.
- Ethonium: a bis-quaternary ammonium compound. The mechanism of action is similar to miramistin (cytolysis due to compromised envelope permeability). It also stimulates wound healing. Available in the form of ointments and solutions. Indicated for trophic purulent ulcers, radiation skin lesions, pruritic dermatoses, stomatitis, gingivitis, as well as corneal ulcers and otitis.
- Cerigel: a combined agent (polyvinyl butyral + cetylpyridinium chloride + 96% ethanol). It has a narrow purpose — it is used exclusively for surgical antisepsis (preoperative treatment of medical staff hands).
- Degmicid: a quaternary ammonium compound used for processing the surgeon's hands and the operative field.