Physical Characteristics of Selected Over-the-Counter Medications

The physical characteristics of over-the-counter medications may be useful to the compounding pharmacist in preparing dosage forms by serving as physical limits for the basis of choice of vehicles and supporting ingredients for formulations. In this study, three bottles of 16 different products were tested for their specific gravity, pH, suface tension and rheological properties. All products tested were heavier than water, with the exception of the lotions. The pH value varied greatly among the products, and the lotions were neutral to slightly acidic; the other preparations were acidic with the exception of Dulcolax and Maalox, which showed a basic pH. Aqueous solutions had a surface tension very close in value to water; all other products that were tested exhibited lower surface tension than water. The viscosity of the products varied greatly; lotions and suspensions demonstrated shear-thinning properties of either plastic or pseudoplastic type; and all solutions had low viscosity similar to that of water, except for Children's Dimetapp and Vicks Nyquil, which showed a somewhat higher viscosity than water.