A History of Isolator and Containment Technology, Part 5: Development and use of sterilising agents with associated devices
In this penultimate section the development of the ‘sterilisation’ of isolators used for sterility testing and aseptic processing will be reviewed.
This will include the chemical agents used, the equipment to deliver and remove that agent (in a gaseous form), as well as agents used for manual wet processes and also fogging techniques with associated equipment.
As mentioned in previous sections of this history the term ‘sterilising’ has been used when related to the ‘sterility’ of isolators1 . A better term perhaps would be ‘biological decontamination’ but the end result of any such decontamination must be to achieve surfaces and other areas such as filters, apertures and other items placed in the treated environment that should be essentially free of microbial life (i.e. sterile).
While some of the agents that will be described have been reported as broad spectrum biocides, their action was initially tested and reported in the liquid phase not as a gas or vapour. The sole exception is formaldehyde which has a long history as a vapour ‘sterilising’ agent for clean rooms, safety cabinets and animal housing. Sterilisation methods in the realm of medical or pharmaceutical uses and which have regulatory approval are all described in some detail in the various pharmacopoeias. There are four main methods:
• Moist steam
• Dry heat
• Irradiation (gamma & e-beam)
• Ethylene oxide gas
As none of these have practical use for isolator sterilisation, other agents were sought and these are listed below in an approximate order of their use. It would be appropriate to mention two other sterilising methods, as agents used for instrument sterilisation have been used in isolators:
1. Low temperature with formaldehyde was used to rapidly sterilise certain instruments, at temperatures ranging from 50°C to 80°C utilising steam. Getinge offered a chamber device based on this type of treatment.
2. Gas plasma sterilisation where the chamber is filled with peracetic acid or hydrogen peroxide vapour under vacuum. After a required exposure time radio frequency energy is applied to the chamber to induce the plasma state in which the active agent is broken down quickly into innocuous parts. This technique is used mainly for instruments and one advantage is that the instrument packs are dry at the end of the cycle. Such a steriliser is the Sterrad® system. […]
A courtesy of ‘Clean Air & Containment Review’ – www.cleanairandcontainment.com
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- author: Thorogood Doug