The sterile filter study should be done to ensure that the process is valid and can be proven as a sterile Filter. The testing itself includes integrity testing, bacteria retention, qualification testing, and extractable and leachable testing.

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Filter Validation Package

Filter validation packages are tailored to meet customer-specific needs and may include some or all of the following:

  • Filter Compatibility Assessment

  • Bacterial Viability / Filter Flush Testing

  • Bacterial Challenge Study

  • Evaluation of Adsorptive Effects

  • Generation of Product Wet Integrity Test Parameters  


Filter Compatibility Assessment
Compatibility testing evaluates filter integrity after exposure to “worst-case” fluid and process conditions. The filter is exposed to the process fluid for a specified period under pre-determined conditions that include: simulated filter sterilization conditions, exposure times exceeding the maximum process time, temperatures exceeding maximum process temperature, and differential pressures that exceed process pressures.

Compatibility is determined by comparing integrity test results using the reference fluid. Tests are performed on the filter prior to and after worst-case exposure. A visual examination for damage or deformation is also conducted.

Bacterial Viability / Flush Testing

Many pharmaceutical products are bactericidal. This test verifies the survival capacity of the organism selected for microbial challenge testing, either in the actual product formulation or a suitable product simulant, for the process time. The appropriate methodology is then chosen for the bacterial challenge study.

Bacterial Challenge Study

This study qualifies the ability of a filter medium to produce sterile filtrate in the process. A solution of the product or simulant is inoculated with the challenge organism at a concentration > 1 x 107 viable organisms/cm2 of filter membrane area. The challenge is performed on three filter membranes from different production batches, with at least one having a pre-filtration physical integrity test value at or near the filter production limit.

Evaluation of Filter Adsorptive Effects

It is critical that filters are selected to minimize adsorption and loss of product components. Laboratory-scale filter tests can be used to generate adsorption profiles to help with filter selections and process qualification.

Product Wet Filter Integrity Test Parameters

Filter integrity tests performed on critical filters immediately before and after batch filtration confirm performance to specification. In order to optimize processing, it may be more convenient to integrity test the filter cartridge wet with the product or process fluid.

Pall Validation Services establish filter integrity test values for process filtration assemblies wet with process fluid. The values are correlated to a reference fluid-wet value (typically water).

The reference fluid-wet value is correlated to bacterial retention information published in the filter validation guide. Product-wet values are then derived from actual test data, not theoretically calculated values, and correspondingly correlated to bacterial retention.

Post-Use Filter Integrity Test

This is an additional service provided by Pall for customers who lack the equipment, materials, or time to integrity test post-use filters at their facility. Damaged capsule filters or vent filters are shipped to Pall to be integrity tested using Pall’s most advanced automated integrity tester. Upon completion, a final report is provided with details of the test conducted, visual observations, integrity test parameters, test results, and a copy of each integrity test printout.