Chemical Disinfectants: Chemical Methods of Sterilization

 Different types of Chemical Disinfectants

•       Alcohols – Ethyl, isopropyl, trichlorobutanol

•       Aldehydes – Formaldehyde, glutaraldehyde

•       Dyes

•       Halogens

•       Phenols

•       Surface active agents

•       Metallic salts

•       Gases – ethylene oxide, formaldehyde

 

MODE OF ACTION OF CHEMICAL DISINFECTANTS:

• Protein coagulation
• Disruption of cell membrane resulting in exposure, damage or loss of the contents.
• Removal of free sulphydryl groups essential for the functioning of the enzymes.
• Substrate competition – a compound resembling the essential substrate of the enzyme diverts or misleads the enzymes necessary for the metabolism of the cell and causes cell death.

ALCOHOLS

• Ethanol (80% v/v ethyl alcohol) or 2-propanol (60-70% v/v iso-propyl alcohol) solutions are used to disinfect skin and decontaminate clean surfaces.
• Spectrum: Effective against fungi, vegetative bacteria, Mycobacterium species and some lipid-containing viruses.

ALDEHYDES

• Formaldehyde: Precautions are required when handling formaldehyde
• Formalin is 37% w/v formaldehyde gas in water.
• Spectrum: Active against most microorganisms.

        Uses of formaldehyde:

• Formaldehyde is used to preserve anatomical specimens, and for destroying anthrax spores in hair and wool.

• 10% formalin containing 0.5% sodium tetraborate is used to sterilize clean metal instruments.

• Formaldehyde gas is used to sterilize instruments, heat sensitive catheters and for fumigation of wards, sick rooms and laboratories.

• It can also be used for clothing, bedding, furniture and books.

• To disinfect equipment such as centrifuges or biosafety cabinets.

        Glutaraldehyde:

• Concentration: Glutaraldehyde is commercially available as 2% w/v aqueous solution which must be made alkaline to "activate" (e.g. by addition of 0.3% sodium bicarbonate).

• Use: for instruments such as cystoscopes, bronchoscopes, corrugated rubber anesthetic tubes, face masks, endotracheal tubes, metal instruments, polythene tubing.

PHENOLS

• Carbolic acids
• Chlorophenols 
• Chloroxyphenols
• Hexachlorphene

Chlorhexidine

• Mainly used for preliminary sterilization of infected glasswares in laboratory, disinfection of excreta, cleaning floors of wards and operation room in hospital.

• Chloroxylenol (dimethyl phenol) is active ingredient of dettol.

• Savlon (chlorhexidine+cetrimide) is widely used in burns, wounds, as bladder irrigant, for surgical instruments and pre-operative disinfection of skin.

• Used as antiseptic. Apply alcoholic chlorhexidine to the skin in the event of accidental contamination.

HALOGENS

        Chlorine Compounds

• Generally used in the form of sodium hypochlorite.

• Concentration: Use at 0.1% as a general disinfectant.

• Uses: It has great widespread use as a laboratory disinfectant on surfaces of bench and in discard spots.

        Iodine Compounds

• Use: Most commonly used for skin disinfection and decontaminating clean surfaces.

FUMIGATION

CONVENTIONAL (FORMALDEHYDE)

• Formaldehyde gas is used for fumigating operation theatres, sick rooms and laboratories.

• Formaldehyde gas generated from a chemical reaction spreads in the room and sterilizes the entire room. The room is kept closed for 48 hours.

• Caution: Formaldehyde can react with free chlorine to produce toxic gas. 

• Remove hypochlorite solutions and hydrochloric acid from spaces to be decontaminated.

• Irritant vapours are released hence neutralize with ammonia following decontamination.

NEWER METHODS OF CHEMICAL DISINFECTANTS:

ETHYLENE OXIDE

• Uses: it has got a good degree of penetration power, even through plastics.

• Plastic goods, polythene tube, artery and bone grafts, cystoscopes, vaccines and culture media can be sterilized by ethylene oxide.

• These objects are kept in a cabinet from which air is removed by a vacuum pump and then a mixture of ethylene oxide and carbon dioxide is introduced in the cabinet.

BETA PROPIOLACTONE

• It is a condensation product of ketone and formaldehyde having a boiling point of 163’C.

• It is capable of killing all microorganisms including viruses.

• Uses: Although BPL has a low penetrating power as a gas, but it is believed to be more efficient for the purpose of fumigation.

• Its biocidal action is very rapid and only 0.2% BPL is used for the sterilization of biological products.

• Limitation: unfortunately BPL has carcinogenic effect.

HYDROGEN PEROXIDE

• A concentration of 3% w/v generally used for disinfection.

• Use: H2O2 is applied to disinfect plastic implants, contact lenses, and surgical prostheses.