A pharmaceutical suspension is a coarse dispersion in which insoluble particles, generally greater than 1 µm in diameter, are dispersed in a liquid medium, usually aqueous.
An aqueous suspension is a useful formulation system for administering an insoluble or poorly soluble drug. The large surface area of dispersed drug ensures a high availability for dissolution and hence absorption. Aqueous suspensions may also be used for parenteral and ophthalmic use, and provide a suitable form for the applications of dermatological materials to the skin.
An acceptable suspension possesses certain desirable qualities, among which are the following:
- the suspended material should not settle too rapidly;
- the particles that do settle to the bottom of the container must not form a hard mass but should be readily dispersed into a uniform mixture when the container is shaken; and
- the suspension must not be too viscous to pour freely from the bottle or to flow through a syringe needle.