A 2007 Q&A by the EMA used the supposedly blocking of a flaw or defect within the filter membrane of a sterilizing grade filter as a reason for the need of a pre-use/post-sterilization integrity test. The filter, being damaged during steam sterilization, would pass the post-use integrity test, due to the fact that the filter flaw is blocked by contaminants. This, "healed" filter would not be detected by the current integrity tests, like diffusion flow or Bubble Point. Questions posted to the agency has not revealed any evidence or data that this truly happened. Filter vendors stated so far that they have not seen such occurrence.
To be sure that this does not happened, tests are performed now with 10" filter elements used in production processes. Around 30 tests of slightly failed filters utilizing different blocking grade of up to 95% showed that such heavily blocked filters will still fail the integrity test. The tests so far have not shown that a filter will "heal" during filtration and post-use testing will be able to find failed filters.
More tests like these are needed to stop speculative regulatory enforcement as it happens with Annex I, paragraph 113 and the 2007 Q&A.
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