INTRODUCTION

The ability of water, or more generally solvents and solutions, to spread to some extent over surfaces in pharmaceutical systems is referred to as wetting. Pharmaceutical systems include drug substances, raw materials, intermediate materials such as blends, formulations, all dosage forms, packaging materials, and devices. In the most direct form of assessing wetting properties, a drop of the test liquid is placed on the surface of the test material (most commonly a solid) while the spreading of the drop is observed optically, as illustrated in Figure 1. The wetting properties of pharmaceutical systems are relevant in manufacturing, dosage form performance, and stability. The purpose of this chapter is to provide the background for wetting properties of pharmaceutical systems, describe the experimental techniques used in pharmaceutical practice, identify the challenges associated with the measurements, and discuss approaches used to modify wetting properties.