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Linda Skowronsky - Articles and news items
Several intrinsic and extrinsic factors influence microbial growth. Two important factors include the presence of available moisture and a supportive temperature. The conditions described in ICH Topic Q1A (R2)1 do not allow the organisms of interest in pharmaceutical solids to grow, due to either an unfavourable temperature or humidity. For this reason, testing either microbial limits or measuring water activity as part of the stability program is considered of little value in determining microbial stability.
An optimised approach for reduced microbial testing to support stability has been proposed2,3. The rationale was given for utilising water activity measurements instead of microbial limit testing on non-aqueous solids with water activity measurements. Many regulatory authorities continue to require microbial limit data although will sometimes accept water activity data to support microbial stability. Quality by Design as described in ICH Q84 emphasises the importance of designing quality into products rather than testing in quality. Therefore, it is important to take a critical view of stability specifications and current testing. Testing typically performed during development is often generated in response to regulators inquiries that consider satisfactory microbial limit and/or water activity data will ensure microbial stability. In the case of materials of low water activity, this conclusion, however, may not accurately reflect in-use conditions.
For decades microbiological quality has remain dormant while the pharmaceutical industry has continued to evolve. Compendial methods and limits, while now generally harmonised throughout the world, still reflect the same methods utilised 100 years ago. Although there is more clarification around the number and types of organisms permitted in products since routes of administration are better defined, there is little change to what is considered an acceptable number or the types of organisms allowed in product. The good news is, however, in this new environment of Quality by Design (QbD) and the Process Analytical Technology Initiative1 outlined in Quality for the 21st Century, application of a Risk Based approach can provide some flexibility for microbial control. Through an enhanced understanding of the product and process gained during product development, some of the repetitive and inefficient end product testing may be replaced with real time or supportive data to confirm microbial quality.
During stability, product testing is performed to ensure the product will continue to meet specified criteria of quality and strength through its expiration or shelf-life at the temperature and humidity required by specific markets. This article will not address the other stability requirement of continued efficacy during consumer use which is done by “in-use testing”, an important subject for another article.
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