How does moisture sorption influence pharmaceutical stability and how is it quantified?

• A. It reduces stability and can promote caking; quantified by UV analysis.
• B. It has no effect on stability and cannot be quantified.
• C. Moisture uptake can promote hydrolysis, polymorphic transitions, and caking; quantified by dynamic vapor sorption or gravimetric moisture analysis.
• D. It only affects packaging color.

Answer: (C)

Moisture sorption matters because water that a solid absorber takes up can act as both a chemical reactant and a physical modifier. Water promotes hydrolysis of susceptible bonds, can drive polymorphic transitions in crystalline forms, and may cause caking or agglomeration that disrupts flow and dissolution. In amorphous materials, water lowers the glass transition temperature and increases molecular mobility, accelerating degradation and phase changes. The amount of moisture absorbed is quantified by measuring sorption as a function of relative humidity, yielding sorption isotherms. Two common approaches are dynamic vapor sorption, which cycles humidity and tracks weight change to produce a sorption curve, and gravimetric moisture analysis, which determines moisture content by weighing the sample before and after drying or by other gravimetric steps.