USP <1112> - Application of Water Activity Determination to Nonsterile Pharmaceutical Products

What it says

This chapter describes how water activity, the amount of water available to microorganisms, can be used to assess the risk of microbial growth in nonsterile pharmaceutical products. It explains how water activity is measured, how it relates to microbial growth limits, and how it can support decisions on product formulation, microbial testing and the need for preservation.

Paraphrased for plain-language clarity. Always verify against the current published regulation text.

What it means in practice

• Low water activity limits microbial growth, so it can be part of the justification for reduced testing.
• Water activity is different from total moisture content, since moisture can be bound and unavailable to microbes.
• Measuring it requires calibrated instruments and consistent technique.

What inspectors look for

• Whether any reduced microbial testing is justified by data.
• Whether measurement equipment is calibrated.
• Whether the data come from appropriate product samples.

Related regulations