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Monday, August 11, 2025

Antiseptic and germicides


Introduction

  • Antiseptics and germicides are chemical agents used to prevent infection by inhibiting or killing microorganisms on living tissue (skin, mucous membranes) or inanimate objects (surfaces, instruments).

  • Antiseptics are formulated for use on living tissues, whereas disinfectants are typically for inanimate surfaces; germicides is a broader term encompassing both.

  • They play a critical role in infection control, wound care, surgical preparation, and general hygiene.

Classification

1. Alcohols

  • Examples: Ethanol (60–90%), Isopropanol (70–90%).

  • Mechanism: Denature proteins and disrupt lipid membranes.

  • Spectrum: Broad – bacteria (including mycobacteria), viruses, fungi; not sporicidal.

  • Uses: Skin antisepsis before injection or minor procedures, hand rubs.

  • Notes: Rapid action, evaporates quickly, inactivated by organic matter.

2. Chlorhexidine

  • Examples: Chlorhexidine gluconate (0.5–4%).

  • Mechanism: Disrupts cell membrane integrity, precipitates cell contents.

  • Spectrum: Gram-positive > Gram-negative bacteria, some viruses, fungi; not sporicidal.

  • Uses: Preoperative skin antisepsis, handwashing, oral rinses.

  • Notes: Persistent activity; avoid contact with meninges and inner ear.

3. Halogens

  • Iodine and Iodophors

    • Examples: Povidone-iodine (Betadine).

    • Mechanism: Iodination of proteins, oxidation of cellular components.

    • Spectrum: Broad – bacteria, viruses, fungi, some spores.

    • Uses: Preoperative skin preparation, wound cleaning.

    • Notes: Less irritation in iodophor form, reduced activity in organic matter.

  • Chlorine Compounds

    • Examples: Sodium hypochlorite (bleach), chloramine.

    • Mechanism: Oxidize cellular components, denature proteins.

    • Spectrum: Broad – bacteria, viruses, fungi, spores (at higher concentrations).

    • Uses: Surface disinfection, water treatment.

4. Hydrogen Peroxide and Peroxygen Compounds

  • Examples: Hydrogen peroxide (3–6%), peracetic acid.

  • Mechanism: Release reactive oxygen species that oxidize cell components.

  • Spectrum: Bactericidal, virucidal, fungicidal, sporicidal at high concentrations.

  • Uses: Wound cleaning, contact lens disinfection, sterilization of instruments (peracetic acid).

  • Notes: Inactivated by catalase in tissues; foam may aid debris removal.

5. Phenolic Compounds

  • Examples: Phenol, chloroxylenol, triclosan.

  • Mechanism: Disrupt cell walls and membranes, precipitate proteins.

  • Spectrum: Bacteria, some fungi, viruses; not sporicidal.

  • Uses: Skin antisepsis (chloroxylenol), healthcare surface disinfection.

  • Notes: Irritant at high concentration.

6. Heavy Metals

  • Examples: Silver nitrate, silver sulfadiazine, mercuric chloride.

  • Mechanism: Bind sulfhydryl groups in proteins, denaturing them.

  • Spectrum: Broad antimicrobial.

  • Uses: Burn wound prevention (silver sulfadiazine), ophthalmic prophylaxis (silver nitrate).

  • Notes: Potential for toxicity; limited systemic use.

7. Quaternary Ammonium Compounds (QACs)

  • Examples: Benzalkonium chloride, cetrimide.

  • Mechanism: Disrupt membrane permeability, denature proteins.

  • Spectrum: Gram-positive, some Gram-negative, enveloped viruses; not sporicidal.

  • Uses: Skin antisepsis, surface disinfection.

  • Notes: Inactivated by organic matter, soaps.

8. Dyes

  • Examples: Gentian violet, methylene blue.

  • Mechanism: Interfere with bacterial cell wall synthesis and protein function.

  • Uses: Antifungal in skin/mucosal infections, Gram staining.

Selection Criteria for Clinical Use

  • Spectrum of activity against expected microorganisms.

  • Speed of action and residual activity.

  • Safety on intended surface (living tissue vs. inanimate).

  • Stability and compatibility with other agents.

  • Resistance potential (low for most antiseptics).

Applications in Healthcare

Skin and Mucous Membrane Antisepsis

  • Surgical site preparation: chlorhexidine-alcohol, povidone-iodine.

  • Hand hygiene: alcohol-based rubs, chlorhexidine washes.

  • Oral care: chlorhexidine mouth rinse.

Wound Management

  • Cleansing and prevention of infection: povidone-iodine, hydrogen peroxide (short-term).

  • Burn care: silver sulfadiazine cream.

Environmental Disinfection

  • High-touch surfaces: chlorine compounds, QACs.

  • Equipment sterilization: peracetic acid, hydrogen peroxide vapor.

Special Uses

  • Ophthalmic prophylaxis (silver nitrate for neonatal conjunctivitis).

  • Water purification (chlorine).

  • Catheter lock solutions (ethanol, taurolidine).

Safety and Precautions

  • Avoid systemic absorption of toxic agents (iodine, mercury compounds).

  • Some agents (chlorhexidine, QACs) may cause allergic reactions.

  • Certain agents (hydrogen peroxide) can damage healthy tissue if used repeatedly in wounds.

  • Always use concentrations recommended for the specific application.

Future Directions

  • Development of broad-spectrum, rapid-acting agents with minimal tissue toxicity.

  • Nanotechnology-based antimicrobials (e.g., silver nanoparticles).

  • Combination antiseptics to broaden spectrum and reduce resistance emergence.

  • Sustained-release formulations for long-term wound care.




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