RAPID STERILITY TESTING

Medicines that have a very short shelf life may require alternative testing strategies for product release. For example, the 14 day growth-based sterility test may not be appropriate for drug products that need to be administered to the patient prior to obtaining the final sterility test result. Products that are most impacted by this challenge include gene and cell therapy or advanced therapy medicinal products (ATMP), positron emission tomographic (PET) drugs and compounded sterile preparations (CSP) produced in a compounding pharmacy.

Fortunately, regulators and compendia have recommended alternative strategies for the testing and release of these types of drug products.

Each of the references discussed below may be downloaded from our References Page.

FDA Final Guidance on Gene Therapy

In January 2020, FDA published its final guidance for industry, "Chemistry, Manufacturing, and Control (CMC) Information for Human Gene Therapy Investigational New Drug Applications (INDs)." The guidance states, “Analytical procedures different than those outlined in the USP, FDA guidance, or Code of Federal Regulations (CFR) may be acceptable under IND if sponsors provide adequate information on test specificity, sensitivity, and robustness.”

Examples of alternative methods, which may be needed for live cells, include rapid sterility tests, rapid mycoplasma tests (including PCR-based) and rapid endotoxin tests. For these non-compendial tests, FDA recommends to qualify/validate them to ensure they are fit for their intended use.

The guidance also states for ex vivo genetically modified cells administered immediately after manufacturing, in-process sterility testing on sample taken 48 to 72 hours prior to final harvest is recommended for product release. This may include a Gram stain and a sterility test compliant with 21 CFR 610.12. Under this approach, the release criteria for sterility would be based on a negative result of the Gram stain and a no-growth result from the 48 to 72 hour in-process sterility test. When the USP <71> sterility test is used, the final product sterility test should incubate for the full 14-day duration, even after the product has been administered to the patient. However, it should be noted that 21 CFR 610.12 allows for the validation of a rapid sterility test, in which case the actual sterility test time to result may be significantly less than 14 days.

EU Guidelines for ATMPs

In May 2018, the EU published its new guidelines for ATMPs, "Rules Governing Medicinal Products in the European Union. Volume 4. GMP. Guidelines on Good Manufacturing Practice Specific to Advanced Therapy Medicinal Products.” The guideline applies to the manufacturing of ATMPs that have been granted a marketing authorisation and of ATMPs used in a clinical trial setting.

The guideline states, "[a]pplication of the sterility test to the finished product (Ph. Eur. 2.6.1) may not always be possible due to the scarcity of materials available, or it may not be possible to wait for the final result before the product is released due to short shelf-life or medical need. In these cases, the strategy regarding sterility assurance has to be adapted.” The guideline recommends to use alternative methods for preliminary results, combined with sterility testing of media or intermediates at relevant time points.

The use of validated alternative rapid microbiological methods according to Ph. Eur. 2.6.27 may also be considered, as long as method suitability for the product has been demonstrated. The guideline also states If the results of the sterility test of the product are not available at release, mitigation measures should be implemented, including informing the treating physician.

Ph. Eur. 2.6.27

European Pharmacopoeia chapter 2.6.27, Microbiological Examination of Cell-Based Preparations, became effective in July 2017. The chapter discusses the characteristics and limitations of cell-based drug products, including a short shelf-life, amounts available for release testing, testing time to result versus patient administration needs, and sampling or technical related issues, such as initial turbidity or antimicrobial activity.

The test sample must be representative of all of the components of the cell-based preparation and be taken from the final preparation. However, where this is not possible, surrogate testing may be performed, for example on the liquids last in contact with the cells being processed. This is similar to the EU guidelines for ATMPs.

Small sample sizes available for testing (due to single donor or manufacturing-related capacities) must still be sufficient to ensure suitable sensitivity and specificity of the test method. As such, the chapter provides recommended test volumes including when to use 1% of the total batch size, which should be decided between the aerobic and anaerobic media (i.e., if a conventional sterility test if employed). But for preparation volumes less than 1 mL, where final sampling is not possible, surrogate testing, in-process testing or other appropriate testing should be used and has to be justified.

The chapter allows for the use of automated growth-based methods or alternative methods, such as a combination of pre-culturing and detection by alternative methods (see chapter 5.1.6), direct detection by alternative methods (see chapter 5.1.6) or other methods based on the harmonized sterility test (see chapter 2.6.1).

When justified for a cell-based preparation with a short shelf life, you may be able to release product based on a “negative-to-date” result, which is an intermediate reading of the sterility test. IN this case, the chapter states that results from additional microbiological in-process control testing may also be needed.

USP Informational Chapter <1071>

USP <1071>, Rapid Microbial Tests for Release of Sterile Short-Life Products: A Risk-Based Approach, became effective in December 2019. The chapter provides guidance when the compendial sterility test is unsuitable for product release due to short shelf life or immediate need, such as compounded sterile preparations (CSPs), positron emission tomographic (PET) products, and gene and cell therapies.

Rapid sterility tests (RSTs) should be risk-based and stakeholders should select their preferred technology considering time to result, specificity, limit of detection (LOD), sample size, and product attributes. The chapter refers to the 1% sampling plan in Ph. Eur. 2.6.27 and provides some examples. The chapter also recommends that rapid sterility tests or other rapid microbiological methods may be used as in-process controls prior to the final product release sterility test to provide early detection of gross contamination or probability that a product may fail sterility.

Finally, the chapter states that setting a limit of detection (LOD) of a single viable cell with all technologies is an unrealistic barrier of entry for any sterility test, especially when the signal is not the colony-forming unit that is amplified by cultural enrichment. We can agree with this but only as long as the method does not have a purported detection sensitivity level of a single cell. For example, some non-growth based rapid sterility tests have proven single cell detection capability (i.e., solid phase cytometry).

As can be seen by the newest policies and compendial recommendations, developing a comprehensive regulatory and validation strategy for ATMPs can be challenging. Our Consulting Team is available to assist with your ATMP rapid sterility test needs.

WE CAN HELP DEVELOP YOUR RAPID STERILITY VALIDATION AND IMPLEMENTATION PLAN

Developing a comprehensive regulatory and validation strategy for rapid sterility testing of short-life drug products can be challenging. Our Consulting Team has practical experience in developing validation protocols that meet compendia recommendations and are accepted by regulatory authorities.

Please CONTACT US to discuss how we may be able to assist you in developing your own rapid sterility testing strategy.