Assay methodologies to serve as alternatives to compendial microbiological methods
USP 1223 Validation of Alternative Microbiological Methods and EP Chapter 5.1.6 Alternative Methods for Control of Microbiological Quality provide guidance on the selection and implementation of assay methodologies to serve as alternatives to compendial microbiological methods. The documents describe important steps that should be taken to evaluate candidate alternative methods, to select the analytical technology and ultimately to qualify the method with actual product. These steps include, but are not limited to:
- Identification of a potentially suitable alternative methodology
- Demonstration that the method is equivalent and applicable as a replacement for a standard compendial method
- Development of user specifications for equipment selection
- Qualification of the method in the laboratory
In addition, the USP 1223 guidance outlines four distinct options for demonstrating equivalence (Download the paper to see Demonstration of Equivalency and Table 2).
Microbiological methods described in the USP 1223 compendia fall into two general categories:
i. Qualitative methods (not enumerative) that are used to assess the general microbial quality of compendial articles. This category includes assays that are intended to demonstrate the absence of microorganisms in the compendial article.
ii. Quantitative methods that yield numerical (enumerative) result in terms of the microbial content of a compendial article.
There are inherent analytical factors that must be considered in the implementation of USP 1223 microbiological methods and in the comparison of a candidate alternative method to an existing compendial method. With respect to qualitative (“absence of”) analysis, it is critical to consider that in microbiology, the finding of “no microorganisms present” does not mean in absolute terms that zero cells are actually present. A result of “no growth” in a current compendial method is properly interpreted as “no growth was detected under the specified conditions”.
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