What is suspension and Criteria for a Good Suspension

SUSPENSIONS

 A suspension may be defined as a heterogeneous ( biphasic ) system comprising of a solid phase ( the dispersed phase ) uniformly dispersed in a liquid phase ( the continuous phase or dispersion medium ) . Apharmaceutical suspension is a coarse dispersion in which insoluble solid particles are dispersed in aliquid medium.

Criteria for a Good Suspension

A good suspension should usually possess the following desirable properties:

(i)Suspended matter should not settle rapidly. 

ii) The particles which settle should not form a hard cake and should redisperse easily on shak- ing.

(iii) A good suspension should not be too viscous to pour. 

(iv) In case of parenteral preparations, the suspension should flow out of syringe needle.

(v) Suspension for external application should be easy to apply and not run off. Also it should not dry off too quickly. 

(vi) A good suspension should have a smooth, elegant appearance.

(vii) It must have an acceptable colour and odour. 

 
(viii) The suspended ingredients should not hydrolyse or degrade too rapidly or undergo change in polymorphic form. Ideally, suspensions should be thixotropic, i., these should become viscous on standing and should thin readily on shaking. This prevents sedimentation of the drug during storage and allows its easy withdrawl on shaking