I am performing several validation tests presently and have a few problems
with microbial recovery and neutralizers. I would appreciate any comments or
suggestions you can provide.
1. I performed an MLT validation on a product containing cefuroxime and have
found out that it would require a dilution of up to 1:10^4 before I can
recover any Gram positive bacteria using the pour plate method, even with
the addition of polysorbate 80 (I only tested up to the 0.2% concentration).
Would serial diluting the product 4 times affect the recovery of possible
contaminants in any way? If so, is there a different method I can apply?
(The product is in tablet form.)
2. Is there a specific method to validate the MLT test for cream products? I
have problems with differentiating "pieces" of cream from my bacteria in the
diluent only control (no neutralizer or surface active agents added) when I
carried out the procedure based on the USP <61> guideline. Again, the pour
plate method was used.
3. When do you add in the neutralizer for the PET validation test? Do you
mix it with the agar media at the time of preparation or would you mix them
at the time of mixing with the product? What concentration range would you
suggest is better for using neutralizers?
I just reailzed I had more questions than I thought. Thank you kindly for
reading through. I hope to hear from you soon.
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