Two examples

Let's start with an example. During validation of an analytical method the linearity should be evaluated. Therefore 5 concentrations with 3 replicates each are examined (in order to evaluate linearity and trueness in one approach). At the examination level corresponding to 120% test concentration, one value is considerably higher than the other two ones. However, even taking this value into account, the acceptance criterion can be met. But the question is what to do. Is it necessary to repeat the entire 120% concentration with all three replicates, are we allowed to exclude the conspicuous one and calculate the mean by using just the two good ones, or do we have to repeat the whole linearity experiment?

For pharmaceutical companies that manufacture their products under aseptic conditions, sterile filtration is the last step before filling. The validation of the manufacturing process also includes the step of sterile filtration. Accordingly, it must be demonstrated by filter validation that the filter is able to retain bacteria and thus ensure the sterility of the product. This evidence is provided by a bacterial challenge test according to ASTM F838-20. But, before this bacterial challenge test can be performed, it must be checked by a viability test that the product solution has no negative effect on the bacterium used in the bacterial challenge test. That sounds complicated? It shouldn’t - just imagine what would happen if your product solution is killing the test bacteria...

A request via our homepage prompted me to focus more intensively on the terms "dilution integrity", "dilution linearity" and "parallelism". They all belong to the area of bioanalytical methods’ validation, i.e. those methods in which a biological sample such as human or animal blood or urine is examined. Such analyzis are needed during the development of drugs in the context of preclinical and clinical studies.

Sterile filters are used in pharmaceutical production, in particular in aseptic manufacturing of parenterals. As part of filter validation, evidence must be provided that the filter used for sterile filtration is able to retain bacteria and potential undesirable components such as particles or fibers, thereby ensuring the sterility of the product. The corresponding test is the bacterial challenge test according to ASTM F838-20. Therefore, the filter is flown with a defined number of particularly small bacteria (Brevundimonas diminuta) in solution and subsequently, the filtrate is examined for bacterial growth. A sterile filtrate shows that the filter is able to retain > 10⁷ CFU/cm² filter surface area and is therefore suitable for its intended use.