Suspension

                                           Suspension                                                                          

A coarse suspension is a dispersion of finely divided, insoluble solid particles (the disperse phase)in a fluid (the dispersion medium).

•Most pharmaceutical suspensions consist of an aqueous dispersion medium although in some instances it may be an organic or oily liquid.
•Physical properties, of a well-formulated suspension:
1)Thesuspensionmustremainsufficientlyhomogenousforatleasttheperiodbetween
shakingthecontainerandremovingtherequireddose.
2)Thesedimentproducedonstoragemustbeeasilyresuspendedbytheuseofmoderateagitation.
3)Thesuspensionmayberequiredtobethickenedinordertoreducetherateofsettlingoftheparticles.Theviscositymustnotbesohighthatremovaloftheproductfromthecontainerandtransfertothesiteofapplicationisdifficult.
4)Thesuspendedparticlesshouldbesmallanduniformlysizedinordertogiveasmooth,elegantproductfreefromagrittytexture.
Pharmaceutical applications of suspensions:

•Suspensions can be used as

1 -Oral suspensions

2 –Reconstitutable suspensions.

3 -Parenteral suspensions.

4-Topical and cosmetic suspensions.

5-Aerosol suspensions.
1. Suspensions as oral drug delivery systems

Many people have difficulty in swallowing solid dosage forms and therefore require the drug to be dispersed in a liquid. Some materials are required to be present in the gastrointestinal tract in a finely divided forms, and their formulations as suspensions will provide the desired high surface area. Solids such as kaolin, magnesium carbonate and magnesium trisilicate, for example, are used for the adsorption of toxins, or to neutralize excess acidity.

The taste of most drugs is more noticeable if it is in an insoluble form. Paracetamol is available both in solution as pediatric paracetamol Oral Solution and also as a suspension. The latter is more palatable, and therefore particularly suitable for children.

2. Suspensions for topical
administration

They can be fluid preparations, such as Calamine Lotion, which are designed to leave a light deposit of the active agent on the skin after quick evaporation of the dispersion medium.

Some suspensions, such as pastes, are semisolid in consistency and contain high concentrations of powders dispersed-usually-in a paraffin base. It may also be possible to suspend a powdered drug in an emulsion base, as in Zinc Cream.
3-Parenteral suspension

Parenteral suspension used for

•Control the rate absorption the drug.

nBy varying the size of he dispersed particles of active agent, the duration of activity can be controlled. If the drug is suspended in a fixed oil such as arachis or sesame, the product will remain after injection in the form of an oil globule, thereby presenting to the tissue fluid a small surface area from which the partitioning of drug can occur. The release of drug suspended in an aqueous vehicle will be faster.

4 –Reconstitutable suspensions.

reach user as a mixture of dry powders dispersed in vehicle (usually water) i.e., reconstituted immediately before use.

nOnce reconstituted, they have limited shelf-lives (weeks)
nUsed for unstable drugs.
nE.g. Dry powder of pediatric antibiotics can stay for long shelf-life, but when formulated as suspension used for 15 days.
5-Suspensions for inhalation
nFor drugs unstable in GIT
nRapid therapeutic effect
nNo first pass metabolism
nLow doses (few side effects)