Chapter 33. Disinfectants and insecticides
At the end of this chapter, the reader should be able to:
• explain what is meant by disinfection and the main types
• list which disinfectants are used on the skin and mucous membranes and explain how to decontaminate the hands
• describe the disinfection of equipment such as bedpans
• identify the agents that are used for wound cleaning
• list the precautions for disinfecting when working with patients with HIV and hepatitis
• list the different types of insecticides and their medical uses and distinguish between the terms ‘cleaning’ and ‘disinfection’
• state the commonly used environmental disinfectants and antiseptics
• state the insecticides in common use and name the conditions which they are used to treat
Disinfectants
Disinfection is the destruction of vegetative bacteria, but not necessarily their spores. Sterilization processes (e.g. autoclaving, gamma irradiation) destroy both vegetative bacteria and spores. However, in most circumstances (e.g. standard ward cleaning procedures, cleaning of bedpans and urinals), a reduction in the total number of bacteria is sufficient to remove the threat of infection to the average patient and disinfection is the appropriate procedure. An exception to this rule is the severely immunocompromised patient nursed in protective isolation. Hospitals have their own protocols for the care of these very vulnerable patients. A good disinfectant is not necessarily a good cleaning agent and the two should not be interchanged.
There are two main types of disinfectant:
• environmental disinfectants, which are used on equipment such as bedpans and urinal bottles
• antiseptics–disinfectants used on living surfaces such as skin and mucous membranes.
These two groups are not substitutes for one another. Environmental disinfectants are often potent chemicals which damage tissue, whereas antiseptics, which have been developed to prevent such damage, not only are too expensive for environmental use but also tend to destroy a narrower range of organisms.
Environmental disinfectants
Phenolic derivatives
Phenol was one of the first disinfectants used and it kills bacteria by destroying their proteins. It has now been replaced because it is not very effective, rapidly losing efficiency with dilution. It is very toxic, causing local corrosion of the mouth, throat and stomach if swallowed, followed by kidney damage.
Commercially available derivatives include Hycolin, which is used as a 2% or 1.5% solution, and Clearsol, which is supplied in sachets to be diluted before use. They are active against a wide range of bacteria, but are unable to destroy most spores and are inactive against some viruses. Phenolics can damage the skin and should be used with protective gloves. They should not be used on food preparation surfaces.
Hypochlorite disinfectants
These disinfectants act by releasing chlorine, the amount released being measured in parts per million of available chlorine. They can be used as environmental disinfectants.
Sodium hypochlorite solution is available in sachet form ( Chlorasol) and diluted as required.
A 1% solution (10 000 parts per million) is used as an environmental disinfectant:
• hypochlorite disinfectants destroy hepatitis B and HIV in a 1% solution
• diluted solutions decay rapidly and must be made up freshly before use.
Glutaraldehyde
Glutaraldehyde solution can be used for sterilizing heat-sensitive instruments such as endoscopes. It is allergenic, toxic and irritant and its use has now been superseded by newer, less toxic chemicals. freshly prepared 2% solution destroys HIV, but is much more expensive than hypochlorites.
Disinfectants used on the skin and mucous membranes (ANTISEPTICS)
Iodine
Iodine is an effective disinfectant which destroys spores as well as vegetative bacteria, but is rapidly inactivated by the tissues. It can also cause skin sensitization. It is now used mainly in the form of povidone–iodine, a non-staining and less irritant complex available as:
• povidone–iodine 10% alcoholic solution
• povidone–iodine 10% (aqueous) antiseptic solution, used for preoperative skin preparation
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