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.

As announced in summer this year and now in more detail in November, ICH's guideline on validating analytical methods will be revised. The content of this guideline comes from two previously separate guidelines merged in 2005, which were published more than 20 years ago. The decision to revise the validation guideline ICH Q2(R1) was made at the ICH meeting in June, together with the decision to create a new analytical procedure development guideline (ICH Q14). Currently, it is unknown whether these will be two separate documents, or whether a combined guideline will result as a possible combination should be examined by the Expert Working Group.