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Even though isolators are designed to prevent contamination from entering them, they still require regular cleaning and disinfection to maintain the required microbial grade. For pharmaceutical isolators this would normally be Grade A, as defined by EC GMP.(1)
Why do we need to consider contamination control?
Research looking at the different types of transfer disinfection procedures used to pass product into isolators show the huge potential for starting materials to be contaminated. It was found that:
The study also showed that, if the transfer disinfection procedure used comprised spraying solely with alcohol, only 27.6% of the spores would be removed. Therefore, there is a potential for contamination to enter the isolator. Even if these figures suggest a move to gassing isolators, the initial bioburden on consumables and surfaces still has to be considered.
Microbial contamination can be broken down into vegetative bacteria, fungi and moulds, viruses and bacterial spores. Bacterial endospores are the dormant state that some bacteria are capable of assuming when environmental conditions place them under stress. They are extremely resistant to destruction by most chemical biocides, heat, UV light, radiation, etc. Thus, they can remain viable and a potential source of contamination over a long period of time.
Cleaning and disinfection methods
Due to the effect of biofilms, surface wiping is needed to assist in the removal of contamination. The correct technique is to wipe towards you, in straight horizontal lines, each time overlapping the previous one by 10–25%. A contaminated wipe should not be passed over an area that has just been wiped. Surface wiping should be carried out from top to bottom, from back to front and from cleanest to dirtiest. The wipe itself should be constructed from a low-particulate material.
Correct cleaning and disinfection can reduce lost batches
One specific factor that should be considered when decontaminating isolator systems using a liquid sanitisation procedure is that all surfaces must be reached. This is not always easy in large or half-suit isolators, but a specially designed tool is now available to solve this problem. Any pads used on cleaning tools should be low-particulate, sterile and disposable. One leading international pharmaceutical manufacturer recently piloted the incorporation of isolator cleaning tools for cleandowns between batches on one cytotoxic production line. The introduction of the tools has resulted in reduced failure rate on vial production on this line, which equates to a saving of €105,000 per week, or €5.46m per annum.
The aim of cleaning is the reduction of the contamination level of the surface to a visibly clean state (ie, remove dust and organic or inorganic soil). This will give a greater likelihood that the disinfectant used will be effective. The effectiveness of the cleaning procedure should be validated, documented and regularly monitored. The same principle also applies to the disinfection procedure. Cleaning should be carried out before and after every manufacturing, preparation or dispensing session and between activities that may result in cross-contamination. Gross soil should be removed with a detergent – a nonenzymatic variety is preferred for isolators. If a detergent is used, a rinsing cycle must be included to remove any residue, which will have an adverse effect on the disinfectant. Rinsing can be carried out with either Water for Injection (WFI), sterile purified or deionised water or sterile alcohol.
Combined cleaning and disinfection
It has been known for many years that alcohol is an effective disinfectant:(3) studies have shown that its efficacy is optimal at concentrations between 50% and 80%.(4) Many institutions use 70% alcohol blends as standard.
Alcohol is suitable as a combined cleaning and disinfection agent, provided no proteins are present, as alcohol will fix these, by a process of protein denaturing, to a surface. The alcohol can be diluted with either WFI, purified or deionised water. If the product contact area requires a disinfectant that is free from endotoxins, alcohol diluted with WFI water should be used. The alcohol used can be either isopropanol (IPA) or denatured ethanol. There is very little difference in efficacy between the two alcohols – the results are almost identical.(5) IPA dries more readily but has a strong acrid smell and a lower occupational exposure limit than denatured ethanol. However, denatured ethanol has a sweeter smell that some users may find unpleasant.
Care should be taken when using alcohol in an isolator as it can have an adverse effect on some materials (eg, some isolator front panels are manufactured from acrylic, which is attacked by alcohol). The crazing effect that can occur over time can be minimised or eliminated by ensuring that surfaces are dried after disinfection and the alcohol or disinfectant is not allowed to accumulate in areas where it cannot be reached. Many disinfectants, especially sporicidal ones, can have an adverse effect on the materials used in the construction of an isolator. Manufacturers should be able to provide information to support the validation of a particular agent.(6)
Why use anything else?
If alcohol has so many benefits, why should we consider anything else? One good reason is that alcohol is not sporicidal, and also GMP Annex 1 states that: “Where disinfectants are used, more than one type should be employed. Monitoring should be undertaken regularly in order to detect the development of resistant strains.”
Disinfectants with different modes of action should be rotated (eg, alcohols disrupt the cell membrane, whereas a quaternary ammonium compound damages the cell wall).
There is a wide range of branded disinfectants available, but they fall into a smaller group of active components. Disinfectants for bacteria and fungi include alcohols, quaternary ammonium compounds, phenols and amphoteric surfactants. None of these have a sporicidal effect.
Sporicidal disinfectants tend to be more aggressive, and many have disadvantages, such as long contact times, health and safety issues or they are corrosive. Sporicidal disinfectants include aldehydes, hypochlorites, hydrogen peroxide/peracetic acid blends and unique formulations such as stabilised chlorine dioxide and quaternary ammonium blends.
When deciding between one disinfectant and another there are six main points to consider:
Many isolator users have problems with degradation of the seals, for example around the hatches. Sterile silicone-impregnated pouch wipes are now available that assist with maintaining good condition of the rubber material. These wipes are supplied sterile and double bagged in easy-tear polythene, so they are suitable for cleanroom use and compatible with transfer protocols. The medical-grade silicone is carried in IPA, which evaporates leaving a thin film of silicone, so it is easy to apply to specific areas and does not leave a sticky residue.