Application of Enzyme Indicators in Hydrogen Peroxide Biodecontamination Cycle Development: A Critical Evaluation of Indicator Variability and Correlation to Biological Indicator Results

An important prerequisite for aseptic production of pharmaceuticals is the appropriate reduction of microbiological contamination. Hydrogen peroxide is commonly applied as decontamination agent for such processes in barrier systems. The development and validation of the barrier decontamination cycles is usually performed with the use of biological indicators (Geobacillus stearothermophilus). However, these indicators inherit certain drawbacks. A new type of indicators became available lately, based on the use of enzyme as a substance decomposed by hydrogen peroxide. There is no broad experience on the practical application of these enzyme indicators yet. Therefore, we investigated the practical use of enzyme indicators in comparison with biological indicators. To broaden the understanding on how these indicators might be used in practice, we provided an evaluation of indicator response variability and the correlation of enzyme indicator results to biological indicator results. In this study, we found the variability of the quantitative enzyme indicator reading to be < 30%, which is much smaller than the variability for spore enumeration of biological indicators (-50% to +300%). Further, we introduced a universal normalization approach to enable convenient comparison and evaluation of different enzyme indicator results. Finally, we discussed a new approach to establish a quantitative correlation between enzyme indicators and biological indicators with the use of threshold values to extrapolate theoretical biological indicator group results. We take the findings of this study as a basis for a suggestion on the practical application of enzyme indicators. We expect that the discussed possibilities of correlating enzyme indicator results to biological indicator results will allow the combined practical use of both indicator types. This would enable the continued application of proven approaches in new ways. Beyond this, the fast reading of enzyme indicators with the gain of significant quantitative information might result in faster and safer qualification and validation of pharmaceutical production equipment in the future.