By Allison Alix, Application Scientist, Lighthouse Instruments
Non-sterile pharmaceutical products, including oral solid dosages (OSDs) such as tablets, capsules, and softgels, are subject to microbiological examination prior to release and during stability testing. USP <61> and USP <62> describe the methods for enumeration and specification of these microorganisms, respectively. While the tests described in these chapters cannot be eliminated from protocol completely, USP <1112>, Application of Water Activity Determination to Nonsterile Pharmaceutical Products, suggests that water activity determination can be used to reduce the need for frequent microbial limit testing and screening, especially for those products with water activities below 0.75. By controlling the water activity of a product, beginning with its raw materials, it is possible to greatly reduce, or even eliminate, the viability of microbial growth.