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Published on 1 January 2005

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Step-by-step selection of cleanroom disinfectants

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Suzanne Stubbs
Quality Consultant
Shield Medicare
Farnham
UK
E:gfroud@shieldmedicare.com

Within the hospital environment, cleanliness is of utmost importance, and nowhere is more critical than the pharmacy production area, where intravenous drugs or parenterals are made for patients. The choice of disinfectants for these controlled areas is a crucial decision, so here is a step-by-step guide to assist you with making this selection.

How to choose a disinfectant
The disinfectants chosen must be able to maintain the low levels of microbial contamination predefined for each class of cleanroom, according to EU standards. Contamination could consist of bacteria, fungi, viruses or bacterial spores. Many disinfectants have a broad spectrum of activity, especially against bacteria. However, most disinfectants are not effective against spores, which pose a particular threat of contamination and are difficult to kill. Some disinfectants that are effective against spores are so aggressive that they may also be harmful to health or equipment, so choosing the right sporicide is especially important. If the disinfectant is to be used in a Grade A zone (isolator or laminar flow cabinet), then it should also be sterile.

Create an environmental history
Air and surface testing of an aseptic area is required under current good manufacturing practice (cGMP). This information identifies the organisms in key areas such as product contact areas, transfer hatches and the outer surface of isolators. An environmental survey provides a basic framework for selecting disinfecting agents and a starting point from which to address specific contamination issues, such as the presence of contamination specific to your cleanroom (facility isolates). Ongoing environmental monitoring then provides an early alarm if contamination levels alter and action needs to be taken.

Establish your disinfectant requirements
Armed with environmental information, the facility can determine what efficacy is needed and can decide on a suitable regime. This should ideally include a rotation of at least two disinfectants. If facility isolates include spores, then a sporicide is essential. Other points to be considered might include:

  • Safety – many disinfectants are toxic or irritant and unpleasant for staff to use.
  • Action time to achieve required kill rate – this can vary from minutes to hours.
  • Range of formats available – for example, ready-to-use, concentrates or impregnated wipes, so that the most convenient and effective method of cleaning can be used.
  • Guaranteed sterility – cGMP states that “disinfectants in Grade A and B cleanrooms should be sterile prior to use”. For products not used in a single session, sterility needs to be maintained once the product is in use.
  • Price – always a key factor, but the calculation of cost needs to include not just the price of the disinfectant, but also costs incurred in time preparing or applying the disinfectant and for protective clothing, wastage and removal of residues.

Select the disinfectants
Traditionally, disinfectants based on phenols and aldehydes have been used, but both these chemicals have disadvantages compared with the latest disinfectants. Phenols are toxic and are ineffective against bacterial spores, so an additional disinfectant would be required. Aldehydes are extremely aggressive and are therefore effective against all microorganisms, but are also highly toxic and require a long contact time for sporicidal activity. Some countries have banned or restricted the use of phenols and aldehydes. There is a wide range of other options available (see Resource). A recent survey showed that alcohol, usually at 70% dilution with water, is widely used for disinfection purposes. This is due to its efficacy against vegetative bacteria, its rapid drying time and the fact that it leaves no residue. However, it is not effective against bacterial spores, so it needs to be used in rotation with an effective sporicide. It is also not suitable for use in large areas due to the operator exposure limits and flammability risk. One of the most recent sporicides available is an alcohol-free blend of a quaternary ammonium compound and stabilised chlorine dioxide. It is nontoxic, nonhazardous and noncorrosive, with a contact time of just five minutes. Its efficacy against spores is suitable for almost all environments, so it presents an ideal solution in many applications.

Testing
The manufacturer of the disinfectant should provide full test and validation data against the standard test methods. Initially, check the manufacturer’s supporting data for your selected agents, including sporicidal activity, as this will identify any additional testing that is required.

Application
Surfaces must be free of dust and physical soiling before disinfection, so that the disinfectant will come into contact with any microorganisms that are present. A sterile neutral detergent is the ideal product for this task.

Due to the effect of biofilms, surface wiping is recommended to assist in the removal of microorganisms.

A wide range of formats are available for the application of a disinfectant, including:

  • Concentrates for use with a mop and bucket system on large areas.
  • Impregnated mop wipes as an environmentally friendly alternative to the mop and bucket system.
  • Ready-to-use sprays or presaturated impregnated wipes for critical areas.

Preventing spore contamination from disinfectants
In most cases, ready-to-use disinfectants are delivered by either trigger sprays or aerosols.  Trigger spray systems offer significant advantages over aerosols. However, there is a problem with some trigger sprays, as contaminated air can be drawn back into the bottle, compromising the sterility of the liquid. Validation work in a licensed pharmacy unit identified that a trigger spray alcohol had become contaminated with fungal spores only eight hours after opening.

A new trigger spray system resolves this problem, providing a system with the benefits of a trigger spray while guaranteeing the integrity of the contents. The new design operates as a closed system, preventing air from being drawn back into the bottle. All points of entry into the bag, including the dip-tube, are completely sealed, thereby creating a closed system.

Case study – French hospital
The cytotoxics unit at a leading French university hospital had been using one of the leading French brands of disinfectant for many years. It was a nonsterile product that was designed to combine the cleaning and disinfection phases (remember that the cleaning should ideally be carried out first in order for the disinfection phase to be fully effective). The unit found this product difficult and time-consuming to mix from sachets of powder, and it also had no sporicidal activity. The chief pharmacist wanted to improve the standards within the unit and was particularly concerned about the presence of spores. The unit has now switched to a sterile neutral detergent for the cleaning phase and a sterile sporicidal disinfectant, Premier Klercide-CR Biocide B, for the disinfection phase. This ensures that it is meeting the cGMP requirement of using sterile products. The use of a cleaning phase means more effective use of the disinfectant and, because the sporicide is neither corrosive nor harmful to health, that the cleanroom environment and the operators are protected.

Resource
A table comparing the properties of different
disinfectants can be obtained by
contacting Shield Medicare:
T:+4412520717616
E:gfroud@shieldmedicare.com



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