chemical disinfection

chemical disinfection

destruction of microorganisms by chemical agents whose effectiveness is determined by concentration (manufacturers' dilution guidelines must be followed exactly to ensure effectiveness), shelf-life (solutions must be used within a finite time after being made up), local environment (e.g. hard water, traces of contaminants [detergents, soap, organic or body tissue, cork, cellulose/cotton wool within the solution]) may all decrease disinfectant effectiveness (Table 1)
Table 1: Types of chemical disinfectant agents
AgentComment
Phenolic compoundsWidely effective against bacteria and fungi; little action against viruses
Used as a 2% v/v solution to disinfect soiled but not blood-contaminated items and a 1% v/v solution for non-soiled items
Inactivated by blood and cationic detergents (not inactivated by other organic materials or anionic/non-ionic detergents)
'Coal tar derivative' types are suitable for floor cleaning
'Pine' types are poor disinfectants and unsuitable for clinical use
Chlorine compounds, e.g. hypochlorites; dichloroisocyanurates (NaDCC)Effective against microorganisms and viruses, including blood-borne viruses
Easily inactivated by blood and organic matter, thus items must be washed first, before being disinfected with chlorine-containing products
Used as 0.1% (1000 ppm) solution routinely in the clinic, but as a 1% solution (10 000 ppm) to clean up after blood spillages
Manufactured as concentrates (10% solutions), powders or tablets which are dissolved as necessary for immediate use
Note:
• 1 volume of 10% concentrate is diluted with 99 volumes of water to form a solution that contains 0.1% (1000 ppm) available chlorine
• 1 volume of 10% concentrate is diluted with 9 volumes of water to form a solution that contains 1% (10 000 ppm) available chlorine
Iodine compoundsAlcoholic solutions of iodine are effective disinfectants, but cause skin irritation and staining
Iodophores (organic complexes containing iodine, e.g. povidone-iodine) are equally effective but less irritant and staining
Iodophores have a wide spectrum of action against bacteria, fungi, viruses and spore forms, and are used for preoperative skin preparation and wound care
AlcoholsEthyl and isopropyl alcohol have a wide spectrum of action and a rapid onset of effect; they are not very effective against viruses
They are prepared as aqueous solutions (70% ethanol in water to 100%; 60-70% isopropyl alcohol in water to 100%)
They are used for the rapid disinfection of clean skin (alcohol hand gels) and hard surfaces (alcohol-impregnated disposable tissues)
They are used in combination with other antimicrobial agents
Biguanide compounds, e.g. chlorhexidineEffective against Gram-positive and Gram-negative bacteria, but poor action against viruses
Their effectiveness is enhanced and more rapid in onset when diluted with alcohol (0.5% chlorhexidine in 70% isopropyl alcohol)
Inactivated by soap and anionic detergent; not recommended for general environmental use
Widely used in skin preparation, as alcohol or cationic detergent-based products
Triclosan (2,4,4'- thrichlor-2'-hydroxydiphenylether)Effective against both Gram-positive and Gram-negative bacteria, with little reported toxicity
Prepared as alcoholic and aqueous solutions
Quaternary ammonium compoundsA group of disinfecting agents with surfactant properties
Active against Gram-positive bacteria, but have little action against other microorganisms
5% Cetrimide mixed with 0.5.% chlorhexidine is used as a wound-cleansing agent
GlutaraldehydeA widely effective disinfectant, with good antiviral and sporicidal action, but which is irritant to skin (thus immersed items should be rinsed in sterile water). It is no longer routinely used in podiatry
For disinfection, the item should be immersed in the solution for 20-30 minutes
For sterilization, the item should be immersed in the solution for 3-10 hours
HexachloropheneEffective against Gram-positive bacteria, but little action against other microorganisms
It has largely been replaced by chlorhexidine or povidone-iodine
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