Local anti-infective agents are substances used on the skin, mucous membranes, or surfaces to destroy or inhibit harmful microorganisms. They include antiseptics, disinfectants, and other chemicals used to reduce infection and contamination.
These agents do not act inside the body; instead, they are applied externally to prevent or control infections.
Important Terms
1. Antisepsis
The process of eliminating disease-causing microorganisms on living tissues. Example: using antiseptics on skin before surgery.
2. Disinfection
Use of chemicals to destroy microorganisms on inanimate objects such as instruments or surfaces.
3. Decontamination
Reduction or removal of harmful microorganisms or dangerous substances.
4. Sanitization
Lowering microbial load on objects to levels considered safe for public health.
5. Sterilization
Complete removal or killing of all forms of microbial life including spores.
6. Pasteurization
Heating food or liquids to 65–100°C to destroy non-spore-forming microorganisms.
Classification of Local Anti-Infective Agents
- Alcohols and derivatives: Ethyl alcohol, Isopropyl alcohol, Ethylene oxide
- Aldehydes and derivatives: Formaldehyde, Glutaraldehyde
- Phenols and derivatives: Phenol, Hexachlorophene, Thymol, Cresol
- Oxidizing agents: Carbamide peroxide, Benzoyl peroxide
- Halogens:
- Chlorine compounds: Halazone, Chlorazodin
- Iodine compounds: Povidone-iodine
- Cationic surfactants: Benzalkonium chloride, Chlorhexidine
- Dyes: Gentian violet, Methylene blue
- Mercurial compounds: Nitromersal, Thiomersal
- Preservatives: Methylparaben, Sodium benzoate
1. Alcohols and Derivatives
Ethyl Alcohol (Ethanol)
Clear, volatile liquid used as an antiseptic and solvent. It is active at 70–90% concentration.
Uses:
- Skin antiseptic
- Preservative
- Mild local anesthetic (due to cooling action)
Isopropyl Alcohol
Stronger bactericidal activity than ethanol. Commonly used for disinfecting skin and instruments.
Ethylene Oxide
A gas used to sterilize heat-sensitive medical equipment. Works by alkylating proteins and nucleic acids.
2. Aldehydes
Formaldehyde
Highly reactive disinfectant used as formalin (37% solution). Acts by alkylating amino, hydroxyl, and sulfhydryl groups in proteins.
Glutaraldehyde
Used for sterilizing instruments. More potent and stable than formaldehyde.
3. Phenol and Phenolic Compounds
Phenol
Oldest antiseptic known. Denatures proteins and disrupts cell membranes.
Uses: Antipruritic, cauterizing small wounds.
Hexachlorophene
Powerful agent active mainly against Gram-positive bacteria. Used in soaps and lotions.
Cresol
Mixture of methyl phenols. Strong disinfectant with unpleasant odor.
Thymol & Eugenol
- Thymol: Mild antifungal; used in dusting powders.
- Eugenol: From clove oil; antiseptic and local anesthetic used in dentistry.
4. Oxidizing Agents
Carbamide Peroxide & Benzoyl Peroxide
Release oxygen that destroys microbes. Used in skin preparations and oral disinfectants.
5. Halogen Compounds
Chlorine Compounds
- Halazone: Used to disinfect drinking water.
- Chlorazodin: Antiseptic releasing chlorine slowly.
Iodine Compounds
Povidone-iodine is a broad-spectrum antiseptic used for skin disinfection before procedures.
6. Cationic Surfactants
Benzalkonium Chloride
Common disinfectant in household products and ophthalmic solutions.
Chlorhexidine
Very effective antiseptic used in mouthwashes, skin cleansers, and surgical scrubs.
7. Dyes
- Gentian Violet – Used for fungal skin infections.
- Methylene Blue – Antibacterial and mild antiseptic.
8. Mercurials
Compounds like nitromersal and thiomersal. Their use has declined due to toxicity concerns.
9. Preservatives (As Local Anti-Infectives)
Some preservatives also act as antimicrobial agents, such as methylparaben and sodium benzoate.
Mechanisms of Action of Anti-Infective Agents
- Protein denaturation
- Cell membrane disruption
- Oxidation of cellular components
- Alkylation of proteins and nucleic acids
- Interference with enzyme activity
Detailed Notes:
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