Antiseptics and disinfectants

Antiseptics vs. Disinfectants - The Clean Up Crew

• Antiseptics: Applied to living tissue (e.g., skin) to inhibit or kill microorganisms. Lower toxicity.

  • Examples: Isopropyl alcohol, chlorhexidine, povidone-iodine.

• Disinfectants: Applied to inanimate objects (fomites) to kill microorganisms. Higher toxicity.

  • Examples: Bleach (hypochlorite), glutaraldehyde, hydrogen peroxide.

• Key Mechanisms:

  • Alcohols/Chlorhexidine: Disrupt membranes, denature proteins.
  • Halogens (Iodine/Chlorine): Oxidation and protein denaturation.
  • Aldehydes: Cross-link and alkylate proteins.

⭐ High-Yield: Alcohols are not sporicidal. For sterilizing equipment contaminated with spores (e.g., C. difficile), an agent like glutaraldehyde or ethylene oxide is required.

Alcohols & Halogens - Potent Liquid Weapons

• Alcohols (Ethanol, Isopropanol)

  • MOA: Denature proteins & disrupt cell membranes. Activity requires water.
  • Use: Skin antisepsis. Optimal concentration is 60-90%.
  • Spectrum: Bactericidal, tuberculocidal, fungicidal, virucidal. Not sporicidal.

• Halogens (Iodine, Chlorine)

  • Iodine & Iodophors (e.g., Povidone-iodine):
    • MOA: Halogenation of proteins and nucleic acids.
    • Use: Pre-operative skin disinfection, wound care.
  • Chlorine-based agents (e.g., Bleach):
    • MOA: Strong oxidizing agents (via hypochlorous acid).
    • Use: Hard-surface disinfection (e.g., C. difficile), water purification.

⭐ Povidone-iodine is an iodophor that acts as a reservoir for iodine, releasing it slowly. This provides sustained antimicrobial action with significantly less skin irritation than elemental iodine solutions (tinctures).

Oxidizers & Biguanides - The Bubble & Stick

• Oxidizing Agents: "The Bubble"

  • Hydrogen Peroxide ($H_2O_2$): Forms destructive hydroxyl free radicals. Used for surface disinfection & cleaning minor wounds. Catalase in tissue creates O₂ bubbles.
  • Iodine/Iodophors (Povidone-iodine): Halogenates proteins. Potent, broad-spectrum agent for surgical site preparation.

• Biguanides: "The Stick"

  • Chlorhexidine: Disrupts bacterial cell membranes, leading to leakage. Binds strongly to skin and mucous membranes (substantivity), providing persistent antimicrobial activity.
  • Uses: Surgical scrubs, oral rinse, central line site care.
  • 📌 Mnemonic: Chlorhex sticks to the skin to hex the germs.

⭐ High-Yield: Chlorhexidine's substantivity (prolonged binding to skin) is key to its efficacy in preventing surgical site and catheter-related bloodstream infections.

Aldehydes & Phenols - The Heavy-Duty Fixers

• Aldehydes (Glutaraldehyde, Formaldehyde)

  • MOA: Alkylate and cross-link proteins & DNA. Potent sporicidal activity.
  • Use: High-level disinfection & sterilization of heat-sensitive equipment (e.g., endoscopes). Formaldehyde for tissue preservation.
  • Tox: Carcinogenic (formaldehyde), potent sensitizers.

• Phenols (Phenol, Chloroxylenol)

  • MOA: Disrupt cell membranes, denature proteins at high concentrations. Bactericidal, fungicidal, virucidal.
  • Use: Surface disinfectants (Lysol), antiseptic in soaps (chloroxylenol). Not sporicidal.
  • Tox: Corrosive; neurotoxicity (hexachlorophene).

⭐ Glutaraldehyde is a chemical sterilant effective against all microorganisms, including spores, making it essential for sterilizing instruments that cannot withstand autoclaving, like bronchoscopes and endoscopes.

High‑Yield Points - ⚡ Biggest Takeaways

• Antiseptics are used on living tissues; disinfectants on inanimate objects.
• Alcohols work by denaturing proteins but are not sporicidal.
• Chlorhexidine disrupts cell membranes and offers excellent residual activity.
• Iodine compounds cause halogenation of proteins and can impact thyroid function.
• Hydrogen peroxide generates oxidizing free radicals; it is sporicidal at high concentrations.
• Quaternary ammonium compounds are cationic detergents inactivated by soaps.
• Phenols disrupt cell walls and can be neurotoxic.