Premature deterioration of a transfer isolator: qualification of a sterilisation time in anticipation of replacing the damaged part.

28 September 2021

Stéphanie Tawil1,} Manon Etis1, Françoise Giraudier1, Marion Lefebvre1, Françoise Cabrera1
1 Pôle Pharmaceutique, CH de Roanne, France

Introduction and purpose
Our rigid isolator installed in 2018 includes a transfer isolator with signs of deterioration (opacity and cracks) in the Poly (methyl methacrylate) (PMMA) walls. Its replacement is planned for September 2021. The duration of the sterilization cycle used routinely was extended compared to the time recommended by the manufacturer (75 versus 60 minutes). The first hypothesis explaining premature wear is overexposure to sterilizing agent (hydrogen peroxide).
The objective of this work is to define and confirm the effectiveness of a shortened sterilization cycle to reduce exposure time of PMMA to H2O2. This is part of the plan to perform qualification of the new transfer isolator.

Material and method
We tested different sterilization cycles of the transfer isolator: 60 - 50 - 40- 30 - 20 - 10 minutes. During these cycles, the transfer isolator contains a load (vials, nozzles, pockets, syringes, etc.) based on a production of 70 preparations per day (maximum production load).
8 bio-indicators (BIs) are required for each sterilization cycle. These are stainless-steel carriers inoculated with 106 Geobacillus stearothermophilus spores. The BIs are placed at critical points in the isolator. Then, at the end of the sterilization cycle, they are inoculated in Tryptic Soy Broth medium and incubated at 55°C. The reading of the culture medium is done at 48h, D7 and D14.
Two types of controls are used: a positive (no sterilization of BI before inoculation) and a negative (culture medium without BI).
To validate a sterilization cycle, three negative inoculation tests are required and to achieve this, the shortest time without bacterial multiplication is repeated twice.

First, among the 6 tested cycles, only the 10-minute cycle was positive for bacterial multiplication.
Then, we tested again the last time without bacterial multiplication: 20 minutes. This test was positive.
Finally, we tested the 30 minutes time twice, no bacterial multiplication was found.

Discussion /Conclusion
We validate the sterilization cycle at 30 minutes and for safety reasons, we will add 10 minutes for our routine sterilization cycle.
This will allow us to reduce the exposure time of the PMMA to H2O2. However, the use of the new module will be subject to a full performance qualification, including the test of the predefined cycle at installation.

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