06.29.20 -- Water Activity Measurements Of Oral Solid Dosage Products

The newly drafted USP <922> General Chapter describes methods for water activity determination in testing protocols. It is water activity, not total water content, that best correlates to critical product quality attributes. USP <922> includes a description of tunable diode laser absorption spectroscopy and states that it is the only method to reliably and accurately measure water activity when the sample contains other volatile compounds.

Water activity determination is increasingly being used in the pharmaceutical industry, as evidenced by a newly drafted USP <922> Chapter for Water Activity measurement. This webcast presents how a water activity measurement can be implemented to give insight into the impact of moisture on critical product quality attributes including stability, dissolution rate, and physical properties of tablets, pills, capsules, and other solid pharmaceutical material.

The draft of the new general chapter USP<922> states that water activity determination can be used to assess the level of protection provided by primary packaging for an oral solid dosage product over its entire shelf life. Water activity measurements provide unique information and complement the data collected from USP<670> Auxiliary Packing Components and USP<671> Containers - Performance Testing.

Non-sterile pharmaceutical products are subject to microbiological examination prior to release and during stability testing. USP <1112>, Application of Water Activity Determination to Non-Sterile Pharmaceutical Products, suggests that water activity determination can be used to reduce the need for microbial limit testing and screening. 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.

Generally, a variety of specific tests are necessary to evaluate the chemical and physical characteristics of an oral solid dosage formulation throughout the product life cycle. This article describes three case studies in which high moisture caused detrimental effects to the potency and/or dissolution of oral solid dosage products. Direct measurements of the product water activity can be used to characterize these effects.

Measuring the water activity at multiple time points during the product life cycle will correlate to changes in critical quality attributes. The FMS-Water Activity Analyzer is a nondestructive headspace gas analyzer used to make direct water activity measurements and quantify relative humidity conditions inside containers.