Integrity testing of filters is a critical step in ensuring the quality and safety of pharmaceutical manufacturing. When dealing with multiple filters, a common question arises: Can multiple filters be tested for integrity together? Different usage scenarios and filter configurations can affect the integrity testing method. Today, let’s delve into the integrity testing of multiple filters.
If filters are used individually, it is generally not recommended to combine them for integrity testing. However, in large-volume filtration, multi-cartridge filter housings may be used for simultaneous filtration. It is usually recommended that integrity testing be performed in situ whenever possible, avoiding disassembly for offline testing. Therefore, in such cases, multiple filters may need to be tested together for integrity.
In Situ Testing
• Filters are installed in the filtration line for integrity testing.
• Integrity testing can be performed at any stage (e.g., post-sterilization, pre-use).
• It can verify the connections of the in situ pipeline.
• The operation is simple.
Diffusive flow or bubble point tests can be used to test large or small filter assemblies. However, the cumulative increase in diffusive flow in larger assemblies (e.g., >30-inch filters or multi-cartridge units) may reduce the practical applicability of the integrity test. Various integrity testing methods (e.g., engineered test systems or diffusive flow detection) can be used to validate specific processes.
One approach is to establish an assembly-specific value for testing multiple filter elements, which is lower than the linearly additive limit. A risk assessment is required to demonstrate the validity of this method. If the diffusive flow of the assembly exceeds the correct limit, the filters can be tested individually to confirm their integrity.
The following are potential risks to consider when applying bubble point and diffusive flow tests to multi-cartridge filtration or large-area filters:
When testing the minimum bubble point of a multi-cartridge assembly, the total diffusive flow may mask the bubble point inflection point of a critical, compromised filter element within the assembly. The observed/measured bubble point of the assembly may be higher than that of the filter element with the lowest bubble point, potentially leading to a false pass result and failing to identify the compromised filter.
Under the specified test pressure, the total gas flow of a multi-cartridge assembly may also mask the abnormally high gas flow of a single compromised filter element. The total diffusive flow may still be below the maximum diffusive flow limit for the assembly (linear superposition limit), calculated by multiplying the number of filter elements in the assembly by the maximum diffusive flow of a single element. This could lead to a false pass result, failing to identify the compromised filter.
TL;DR: Summary in a Few Sentences
• Provided the test method is validated, the bubble point test should be selected first.
• If the bubble point value cannot be stably measured (bubble point test is not applicable), a diffusive flow value lower than the linear superposition limit may be used, but the specific diffusive flow value must be validated.
• A linearly superimposed diffusive flow value may also be used, but test validation is required to assess feasibility.