ABSTRACT
The physical, chemical, and mechanical properties of pharmaceutical drugs and dosage forms are critically dependent on the presence of moisture. Although the properties of individual solids and the performance of solid dosage forms are dependent on moisture, characterization of the underlying water–solid interaction is often nebulous. It is the objective of this entry to highlight various mechanisms whereby water can interact with solid substances, present methodologies that can be used to obtain the necessary data, and then discuss moisture uptake for non-hydrating crystalline solids below and above their relative humdities for amorphous solids and for pharmaceutically processed substances. Additionally, transfer of moisture from one substance to another is reviewed.
