Mechanism of action and classification
The antimicrobial action of these compounds (from Lat. detergere — to cleanse, wipe away) 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 nutritional 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 particular group is of the greatest interest to medicine, as it possesses a much more powerful antiseptic potential.
Pharmacology of cationic detergents
Cationic detergents work at the cellular level: they tightly bind to 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 excellent destroy Gram-positive (G+) bacteria, however, they act rather weakly on Gram-negative (G-) flora.
- Static action: they stop the growth and reproduction of fungi (fungistatic effect) and bacterial spores (sporostatic effect).
Factors reducing efficacy: It is important for the physician to remember that the antiseptic potency of cationic detergents drops sharply under unfavorable conditions. These include:
- Presence of organic substrates (abundant pus, blood in the wound).
- Presence of metal ions (calcium, magnesium, iron, aluminum).
- Joint use with anionic soaps (direct chemical antagonism occurs).
Main areas of application:
- Strict antisepsis of the surgeon's hands and preparation of the surgical 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 (Rokkal): a cationic detergent with antibacterial, antiprotozoal, and spermicidal action. The latter effect is due to damage to the sperm membrane, which makes fertilization impossible (used in gynecology as local contraception in the form of creams, tablets, and suppositories). It is also used externally for the treatment of wounds, trophic ulcers, and irrigation of cavities (urethra, urinary bladder). Safety issue: in a number of countries, the drug is not recommended as an antiseptic. Outbreaks of nosocomial infections have been registered, since 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 state 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 envelope permeability disturbance). It also stimulates wound healing. It is 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 combination agent (polyvinyl butyral + cetylpyridinium chloride + 96% ethyl alcohol). It has a narrow purpose — used exclusively for surgical antisepsis (preoperative treatment of medical personnel's hands).
- Degmicide: a quaternary ammonium compound used for the treatment of the surgeon's hands and the surgical field.
To remember the factors reducing the action of cationic detergents, use the "OMA" rule: Organics (pus, blood), Metals (Ca, Mg, Fe, Al), Anionic soaps.
Class and exam questions
Why cannot cationic detergents be used together with regular soap?
Regular soap belongs to anionic detergents. When used together with cationic drugs, pharmacological antagonism arises, and the antiseptic effect is completely neutralized.
What is the danger of using benzalkonium chloride in a hospital setting?
Gram-negative bacteria, in particular Pseudomonas aeruginosa, can survive and multiply in its solutions. This can lead to severe outbreaks of nosocomial infections.
How does benzalkonium chloride work as a contraceptive?
The drug exerts a pronounced spermicidal effect: it irreversibly damages the cell membrane of spermatozoa, depriving them of the ability to fertilize the egg.
What else to study on this topic
- Comparative characteristics of anionic and cationic detergents
- Application of detergents in surgical practice and combustiology
- Spermicidal agents: the role of detergents in local contraception
- Drugs stimulating tissue regeneration (Miramistin and ethonium)
- Features of medical instrument disinfection with detergents
Master the entire topic in the «Pharmacology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic «Detergents» and 5,304 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 116 video lessons on the subject
Other topics in the section «Antiseptics and Disinfectants»
Free video lessons: pharmacologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.