Acids and alkalis

General pharmacodynamic effects

The antimicrobial activity of acids and alkalis is based on their ability to shift the hydrogen ion index at the application site. In addition to directly destroying bacteria and fungi, these substances exert a pronounced effect on host tissues.

It is important to note that the interaction of alkaline compounds with living tissues has certain specific features. When applied to the skin or mucous membranes, alkalis react chemically with tissue proteins. As a result of this process, so-called albuminates are formed, which have a loose structure (unlike compounds caused by acids).

Due to this property, alkaline solutions effectively:

• soften the epidermis;
• dissolve viscous mucus, mucin, and accumulations of inflammatory exudate;
• reduce local acidosis by shifting the pH and noticeably decrease tissue edema;
• promote mechanical flushing and removal of pathogenic fungal mycelium.

The use of weak alkaline solutions causes mild tissue irritation, leading to improved trophic support (nutrition).

Acid preparations

In modern medical practice, two acid preparations with proven antiseptic activity are most commonly used:

1. Boric acid. This drug is characterized by a dual spectrum of action: it exerts both antibacterial and antifungal (fungistatic) effects. The choice of dosage form depends on the indications. Aqueous solutions are traditionally used for eye washing in the treatment of conjunctivitis, as well as for treating affected areas in skin dermatitis. Alcoholic solution is a classic remedy for the treatment of acute and chronic otitis media. In addition, boric acid is an important component of such well-known combination drugs as Fukortsin and Boromenthol.

1. Salicylic acid. This agent is distinguished by a great variety of dosage forms: ointments, pastes, powders, and alcoholic solutions are available. Pharmacodynamics includes antiseptic, as well as irritating and counterirritant effects. Of particular note is its keratolytic action — the ability to soften and cause rejection of the stratum corneum of the epidermis, which is prominently manifested exclusively when using the drug in high concentrations. The main indications for prescription are infected skin lesions, seborrhea, hyperhidrosis (excessive foot sweating), and the need for corn removal. It is part of many combination products: corn liquid, Salipod corn plaster, Lassar's paste, Galmanin powder, and Diprosalic ointment.

Alkali preparations

The group of alkalis is represented by a number of compounds widely used for external treatment, gargling, and specific neutralization:

• Sodium bicarbonate (Sodium bicarbonate). Acts as a weak antiseptic. Used exclusively externally in the form of washings and inhalations. Main indications include inflammatory processes of mucous membranes (rhinitis, stomatitis, conjunctivitis, tonsillitis). The solution is also indispensable for the rapid neutralization of damaging agents (acids or toxic substances) upon contact with mucous membranes.
• Sodium tetraborate (Sodium tetraborate). It exhibits a pronounced bacteriostatic type of action. Its main feature is high specific activity against yeast-like fungi of the genus Candida. The drug effectively removes the mycelium, disrupts the process of fungal attachment to the mucous membrane, and inhibits its further reproduction. It is prescribed in the form of rinses and applications for candidiasis of various localizations (oral cavity, pharynx, upper respiratory tract, urogenital tract), as well as for the treatment of diaper dermatitis and bedsores.
• Ammonia (Ammonia). Its mechanism of action stands out in this group: it causes protein coagulation, which provides a powerful bactericidal effect. The pharmacodynamics of ammonia combines an antiseptic action with a strong irritant effect due to the stimulation of sensory nerve endings. It is used in the form of liniments and lotions. It is indicated for the treatment of myositis and neuralgia (as a counter-irritant), as well as for neutralizing acidic toxins in insect and snake bites.
• Calcium hydroxide (Calcium hydroxide). By its chemical nature, it is a strong base. It exerts a pronounced antiseptic effect and effectively inhibits inflammatory processes in the dental pulp. The drug is of immense importance in dentistry: it is used for the disinfection of root canals, and also actively stimulates the regeneration and mineralization of dental tissues.

Class and exam questions

What else to study on this topic

• The mechanism of loose albuminate formation upon contact of alkalis with tissues.
• Keratolytic action of salicylic acid: dependence of the effect on concentration.
• The use of calcium hydroxide in endodontics and the treatment of pulpitis.
• Comparative characteristics of the fungistatic action of boric acid and sodium tetraborate.
• Combination drugs based on salicylic acid (Lassar's paste, Diprosalic).

Other topics in the section «Antiseptics and Disinfectants»

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