The Ask the Experts feature on the EMDM and Medical Device Technology magazine home pages continues to broaden in scope. One of the newest recruits, Peter Strain, Vice President, Technology, EMEA, at Sterigenics (Leuven, Belgium) is fielding questions involving sterilisation. One user recently posted the following query: My product’s ethylene oxide (EtO) residue does not meet the new standard ISO 10993/7. Do I need to validate a new cycle, or is there another way without just extending quarantine time?
To achieve the minimum aeration quarantine time necessary to meet ISO 10993/7, replies Strain, there are two possible options: validation of a new cycle or use of dynamic aeration.
Validation of a new cycle: Minimising the impact and cost of a new cycle design is important, so creating an optimised version of an existing cycle can be beneficial in that it means that any product and packaging functionality data may continue to be valid. If this approach is used, the key process parameter that should be optimised is EtO gas dwell time. In order to reduce this to the minimum necessary to achieve the required product sterility assurance level (SAL), a change of validation method may bring significant benefits. If the product SAL has been established using the so-called half-cycle approach (ISO 11135-1:2007 Annex B.1.2 a), which is regarded as an overkill method, a reduction in gas dwell time is best achieved by changing to the methods described in Annex A. These methods quantify the deactivation rates and allow a more targeted SAL to be selected, which will in turn permit a shorter gas dwell to be used in routine sterilisation. This reduction in gas dwell time is likely to reduce product residue levels and therefore permit the use of shorter aeration times. It is a good idea to perform an initial qualification experiment to quantify potential benefits before embarking on a full requalification exercise.
Use of dynamic aeration: Traditionally, products sterilised by EtO are quarantined in aeration at a controlled temperature for a defined time until the product residue levels comply with the limits specified in ISO 10993/7. Dynamic aeration is a more efficient way of outgassing products and can bring significant reduction in the traditional aeration time. It is best performed in the sterilisation chamber and involves the use of combinations of vacuum levels and holds and air/other gas washes that are selected based on product design and the materials used. This method will increase the residence time in the sterilisation chamber; the associated costs must be balanced against the reduction in traditional aeration time.