Water Content has long been recognized as an important parameter in pharmaceuticals for determining product safety and stability. While water activity (aw) has been extensively used in the food and cosmetic industries to prepare products with a low risk of microbial contamination, it is relatively new to pharmaceuticals and should be employed in the consumer health and pharmaceutical industries. As proposed by United States Pharmacopoeia (USP) Method <1112> Application of Water Activity Determination to Nonsterile Pharmaceutical Products, measurements of water activity may provide a faster and more accurate window into microbial effects, preservation, and shelf life. Water activity not only provides the tool and rationale for reducing the frequency of microbial limit testing, it also aids in formulating naturally preserving systems and relates directly to a product's chemical and physical stability.
Pharmaceutical manufacturers prefer to err on the side of over-preserving and tend to over-test their products irrespective of the risk of microbial contamination. However, measuring water activity can be more than just another test; it can provide the scientific justification to exclude microbial limit testing from the specification. Water activity determination is a powerful tool that can be applied during product development to assess the ability of in-process materials and finished products to support microbial growth ... USP Method <1112> using water activity provides a powerful tool in determining the microbial effects, preservation, and shelf life of pharmaceutical products. This tool is best applied during product development and will highlight whether microbiological attributes are critical quality parameters. Products that because of their reduced water activity will not be susceptible to microbial growth are good candidates for the elimination of routine microbial testing. Water activity not only provides the tool and rationale for reducing the frequency of microbial limit testing, it also aids in formulating naturally preserving systems and relates directly to a product's chemical and physical stability.