_____ are pharmaceutical liquid preparations containing solid drug particles dispersed in a liquid medium in which the particles are not soluble.

• A. Solutions
• B. Emulsions
• C. Gels
• D. Suspensions

Answer: (D)

This describes a suspension. In a suspension, solid drug particles are dispersed throughout a liquid and the drug is not soluble in that liquid, so the particles remain as discrete solid pieces rather than dissolving into the medium. Because the particles are insoluble, they can settle out under gravity over time, which is why suspensions need shaking before use to re-disperse the drug and ensure uniform dosing. Stability hinges on particle size, density, viscosity, and the use of suspending agents to slow sedimentation and keep a uniform mix.

This differs from a solution, where the drug is completely dissolved at the molecular level and the mixture is homogeneous and clear. It also differs from an emulsion, which is a mixture of two immiscible liquids with droplets of one phase dispersed in the other, and from a gel, which is a semi-solid where a three-dimensional network traps liquid.