Antimicrobial action of alcohols

Mechanism of action and application of alcohols

The main representative of the alcohol group in medical practice is ethyl alcohol (ethanol). Its antimicrobial activity is non-linear: to achieve the maximum antiseptic effect, a strictly defined concentration is required — from 70° to 80°.

The mechanism of action of ethanol consists of two main processes:

1. Protein denaturation — alcohol irreversibly alters the spatial structure of protein molecules in the microbial cell.
2. Membrane damage — the agent disrupts the integrity of cell walls, leading to the death of the microorganism.

In clinical practice, ethanol is traditionally used for skin preparation: disinfection of the surgical team's hands, treatment of the surgical field, and disinfection of skin areas before injections.

The place of alcohols in the chemical classification of antiseptics

Alcohols are just one of many groups of antimicrobial agents. The global classification of disinfectants and antiseptics is based on their chemical structure. In addition to ethanol, the physician's arsenal includes:

• Halogen-containing compounds. These include iodine preparations (5% alcohol solution, Lugol's solution, iodoform) and chlorine. Organic chlorine-containing agents, such as tosylchloramide sodium (containing 25–29% active chlorine), perfectly deodorize and disinfect patient excreta, but are suitable only for non-metallic instruments due to the risk of corrosion.
• Oxidizing agents. These include 3% hydrogen peroxide solution (Solutio Hydrogenii peroxydi diluta), the combination drug urea hydrogen peroxide, and potassium permanganate (used in concentrations from 0.02% for cavity irrigation to 5% for burn treatment).
• Phenols and tar derivatives (resorcinol, lysol, hexachlorophene). They coagulate proteins and disrupt membrane permeability, but their use today is limited due to toxicity and irritating effects.

Comparison of mechanisms of action

To better understand the specifics of alcohols, it is useful to compare their action with other chemical classes. Each group has its own unique targets in the microbial cell.

For example, aldehydes (formaldehyde) possess powerful bactericidal, sporicidal, and virucidal effects, allowing them to be used for instrument sterilization. Detergents (chlorhexidine, miramistin) integrate into the lipid layer of the bacterial membrane, disrupting it. Meanwhile, heavy metal salts (silver, zinc, copper preparations) bind to sulfur within the amino acid cysteine, causing protein coagulation.

Alternative drug groups

When the use of classical chemical antiseptics is limited, other groups are used:

• Synthetic derivatives. Nitrofurans (furatsilin) disrupt nucleic acid synthesis by reducing their nitro group. Quinoxaline derivatives (dioxidine) and 8-hydroxyquinoline derivatives (nitroxoline) are also used.
• Herbal preparations. Created on the basis of extracts. For example, an alcoholic solution of chlorophyllipt contains a sum of aldehyde-phenol compounds from eucalyptus leaves, providing antibacterial, anti-inflammatory, and weak fungistatic effects.
• Dyes. Brilliant green or methylene blue are active primarily against gram-positive flora; however, their significant drawback is a sharp decrease in antimicrobial activity in the presence of organic substrates (blood or pus).

Class and exam questions

What else to study on this topic

• Halogen-containing compounds: differences in the application of iodine and chlorine preparations.
• Oxidizing agents in surgery: the role of hydrogen peroxide and potassium permanganate.
• Detergents (Surfactants): the spectrum of activity of chlorhexidine and miramistin.
• Heavy metal salts: the cauterizing action of silver nitrate and the use of colloidal preparations.
• Synthetic derivatives: the mechanism of action of nitrofurans and quinolones.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.