Sterility Testing USP (71)

Nova provides USP Sterility testing of pharmaceuticals, radiopharmaceuticals, medical devices, and water. Sterility testing is required during the sterilization validation process as well as for routine release testing. Nova provides all three USP Sterility Methods:

1) Membrane Filtration

2) Direct Transfer (Product Immersion)

3) Product Flush.

NEW Amendments to Sterility Test Requirements for Biological Products Final Rule – 21 CFR Parts 600, 610, and 680

FDA issues a final rule on sterility testing of biological products providing greater flexibility for development of sterility test methods. The purpose of the amendments is to:

  • Promote improvement and innovation in the development of sterility test methods,
  • Address the challenges of novel products that may be introduced to the market in the future, and
  • Potentially enhance sterility testing of currently approved products.

Nova can provide all of these services in addition to traditional USP Sterility Testing.

Membrane Filtration Sterility Testing

The Membrane Filtration Sterility Test is the method of choice for pharmaceutical products. An appropriate use of this test is for devices that contain a preservative and are bacteriostatic and/or fungistatic under the direct transfer method. With membrane filtration, the concept is that the microorganisms will collect onto the surface of a 0.45-micron pore size filter. This filter is segmented and transferred to appropriate media. The test media are fluid thioglycollate medium (FTM) and soybean casein digest medium (SCDM). FTM is selected based upon its ability to support the growth of anaerobic and aerobic microorganisms. SCDM is selected based upon its ability to support a wide range of aerobic bacteria and fungi (i.e., yeasts and molds). Incubation time is 14 days.

Direct Transfer Sterility Testing

This method is the method of choice for medical devices because the device is in direct contact with test media throughout the incubation period. Viable microorganisms that may remain in or on a product after sterilization have an ideal environment within which to grow and proliferate. This is especially true with damaged microorganisms where the damage is due to a sub-lethal sterilization process. All microorganisms have biological repair mechanisms that can take advantage of environmental conditions conducive to growth. The direct transfer method benefits these damaged microorganisms. The entire product should be immersed in test fluid. With large devices, patient contact areas should be immersed. Large catheters can be syringe filled with test media prior to immersion. Nova understands that appropriate modifications are required due to the size and shape of test samples. The method requires that the product be transferred to separate containers of both FTM and SCDM. The product is aseptically cut, or transferred whole, into the media containers. After transferring, the samples are incubated for 14 days.

Product Flush Sterility Testing

The product flush sterility test is reserved for products that have hollow tubes such as transfusion and infusion assemblies where immersion is impractical and where the fluid pathway is labeled as sterile. This method is easy to perform and requires a modification of the FTM media for small lumen devices. The products are flushed with fluid, and the eluate is membrane filtered and placed into FTM and SCDM.

Bulk Drug Products / Biologics and Pharmaceuticals

Bulk Pharmaceuticals (APIs) are tested for sterility per USP 71 before release to the manufacturing processes. Bulk Biologics are tested according to 21 CFR 610.12 for sterility testing. This method requires one media (FTM).

Suitability and Validation

The USP Sterility Test contains two qualifying assays which must be performed. They are the “Suitability Test” (Growth Promotion Test) and the “Validation Test” (Bacteriostasis and Fungistasis Test).

The Suitability Test – is used to confirm that each lot of growth media used in the sterility test procedure will support the growth of fewer than 100 viable microorganisms. If the media cannot support the growth of the indicator organisms, then the test fails. Secondly, a portion of each media lot must be incubated and assessed for sterility according to the incubation parameters (time, temperature) established by the method. If the media is found to be non-sterile, then the test fails.

The Validation Test – is used to determine if the test sample will inhibit the growth of microorganisms in the test media. Stasis, regarding microbiology, is defined as the inability of a microorganism to grow and proliferate in microbiological media. Media that is bacteriostatic does not necessarily kill bacteria; it simply may inhibit bacterial growth and proliferation. The Validation Test must be performed on each product before and/or during sterility testing. This test determines if the media volumes are valid for the particular product. Some medical products contain bacteriostatic and fungistatic compounds that may require special procedures and special media for testing. This test is similar to the Suitability Test described above, however, the product sample is placed in the media along with the microorganisms. Microbial growth in the presence of the test samples is compared to controls without test samples. If microbial growth is present in the sample and control containers, the test is valid. Suitability, validation and sterility tests can be performed simultaneously.

Interpretation of Sterility Test Results

During the incubation period, the media is viewed for growth. The media should be clear and transparent against a light source. Turbid (cloudy) areas in the media are indicative of microbial growth. Once growth is detected, the suspect vessel is tested to confirm that the turbidity present is due to microorganisms and not due to disintegration of the sample; sometimes samples produce turbidity because of particulate shedding or chemical reactions with the media. Once a suspect container has been tested, it should be returned to the incubator for the remainder of the incubation period. Samples that render the media turbid are transferred on Day 14 of the test and incubated for four days. Growth positive samples require further processing such as identification and storage.

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