Chemical Methods of Sterilization

Chemical Methods: Aldehydes & Alcohols - Potent Potions

• Aldehydes: Alkylate proteins & nucleic acids
  • Formaldehyde:
    • Gas; Formalin (37% aq. sol.)
    • Uses: Fumigation, vaccine prep, tissue preservation (10% formalin)
    • ⚠️ Carcinogenic, irritant
  • Glutaraldehyde:
    • 2% sol. (Cidex), alkaline pH activated
    • HLD: 20-90 min; Sterilant: 6-10 hrs
    • Uses: Endoscopes, heat-sensitive items
    • Less irritant vs formaldehyde

⭐ Glutaraldehyde (2%): Sterilization 6-10 hrs; HLD 20-90 mins.

• Alcohols: Denature proteins, disrupt membranes
  • Ethanol, Isopropanol (60-90%, opt. 70%)
  • Uses: Skin antisepsis, surface disinfection
  • Rapid acting; Not sporicidal
  • ⚠️ Inactivated by organic matter; damages rubber/plastic
  • 📌 "Alcohol cleans, spores remain."

Chemical Methods: Halogens & Phenolics - Clean Scene Agents

• Halogens: Oxidizing agents; broad-spectrum.
  • Iodine:
    • Mechanism: Iodination & oxidation of proteins.
    • Forms: Tincture (Iodine in alcohol), Iodophors (e.g., Povidone-Iodine - sustained release, less irritating).
    • Uses: Skin antisepsis, disinfection. Sporicidal (prolonged contact).
  • Chlorine:
    • Mechanism: Forms hypochlorous acid ($HOCl$) in water.
    • Forms: Sodium hypochlorite (Bleach: 0.5-1% general, 5% spills), Chloramines.
    • Uses: Water/surface disinfection. Sporicidal.

    ⭐ Dakin's solution (0.5% sodium hypochlorite) is used for wound irrigation.

• Phenolics: Disrupt cell membranes, denature proteins.
  • Examples: Phenol (carbolic acid), Cresols (e.g., Lysol), Chloroxylenol (Dettol).
  • Activity: Bactericidal, fungicidal, virucidal (enveloped). Not sporicidal.
  • Stable in organic matter. 📌 "Halogens Clean Incredibly": Halogens, Chlorine, Iodine. and Phenolic compounds sterilizing medical equipment)

Chemical Methods: Oxidizing Agents & Gases - Vapor & Vigor

• Oxidizing Agents: Oxidize cell components.
  • $H_2O_2$: Free radicals. Uses: Skin (3%), instruments (7.5%), VHP. No toxic residue.
  • Peracetic Acid ($CH_3COOOH$): Denatures proteins. Sporicidal. Uses: Instruments (0.2-0.35%). Rapid. Corrosive.
• Gaseous Sterilants: For heat-labile items.
  • Ethylene Oxide (ETO): Alkylation. Penetrative. Conditions: 450-1200 mg/L, 30-60°C, 4-18 hrs. Toxic, needs aeration. 📌 ETO: Ensure Thorough Out-gassing.
  • $H_2O_2$ Gas Plasma: Ionized $H_2O_2$ free radicals. Temp <50°C, cycle <1 hr. Fast, non-toxic byproducts.

⭐ ETO sterilization demands prolonged aeration (8-12 hrs) for heat-sensitive items due to its toxicity/carcinogenicity.

Chemical Methods: Surface Agents & Others - Surface Sentinels

• Surface-Active Agents (Surfactants): Disrupt cell membranes.
  • Cationic (QACs): Cetrimide, Benzalkonium Cl. Gram(+), enveloped viruses. Inactivated by soap/organics. 📌 QACs: Cationic.

    ⭐ QACs (e.g., Cetrimide) are inactivated by organic matter & soaps; Pseudomonas aeruginosa often resistant.

  • Anionic (Soaps): Cleansers, weak Gram(+) activity.
  • Amphoteric (Tego): Broad spectrum, low toxicity.
• Dyes:
  • Aniline (Crystal Violet): Gram(+), fungi.
  • Acridine (Proflavine): Antiseptic.
• Metallic Salts: Oligodynamic action (protein/enzyme damage).
  • Silver (Ag): $AgNO_3$ (ophthalmia neonatorum prophylaxis), Silver sulfadiazine (burns).
  • Mercury (Hg): Thimerosal (preservative, historical).
  • Copper (Cu): $CuSO_4$ (algaecide, fungicide).
• Acids/Alkalis: Extreme pH denatures proteins. Organic acids (food preservatives).

High‑Yield Points - ⚡ Biggest Takeaways

• Glutaraldehyde (2%): High-level disinfectant & sterilant (6-10h for spores); used for endoscopes.
• Ethylene Oxide (ETO): Gaseous sterilant for heat-labile items (e.g., plastics, catheters); toxic, requires aeration.
• Hydrogen Peroxide Vapor/Plasma: Sterilizes heat-sensitive equipment; no toxic residues, rapid.
• Peracetic Acid (0.2%): Rapid sterilant (effective in <30 min), even against spores; corrosive.
• Formaldehyde: Gaseous sterilant for fumigation (OTs); carcinogenic, less preferred.
• Alcohols (70%): Intermediate disinfectants (not sporicidal); skin antisepsis, disinfect surfaces.