Suspensions

Dosage forms

Suspensions

Introduction

Suspension is the dispersion of a solid in a liquid or gas. A pharmaceutical suspension is the dispersion of solid particles (usually a drug) in a liquid medium (usually aqueous) in which the drug is not readily soluble. This dosage form is used for providing a liquid dosage form for insoluble drugs. The particle size of the dispersed phase in most of the oral pharmaceutical suspensions is between 1 and 50 μm. The lower the particle size, the larger the surface area of the suspended drug. Lower particle size allows the for-mation of a uniform, fine particle suspension with low grittiness and high redispersibility. A larger surface area of the dispersed drug promotes rapid drug dissolution on dilution with biological fluids upon administration.

Aerosols, suspensions of a solid or a liquid in a gas (e.g., air), are special-ized dosage forms used for pulmonary drug delivery. These dosage forms are discussed in Chapter 15.

In addition to the use of aqueous pharmaceutical suspensions as drug products, suspensions are also used as in-process materials during indus-trial pharmaceutical manufacturing. For example, tablets are coated with a suspension of insoluble coating materials. Granules manufactured by wet-granulation processes are typically suspended in the air for drying dur-ing fluidized bed-drying process. In addition, wet granulation could be carried out on granules suspended in the air in a process called fluid-bed granulation.