Pharmaceutical suspension = a coarse dispersion in which
finely divided solid particles are dispersed is a liquid medium.
IMPORTANCE:
Ø Suspensions
supply insoluble and often distasteful substances in a form which is pleasant
to the taste.
Ø Suspensions
provide suitable forms of application of dermatological materials to the skin
and mucous membranes
Ø Suspensions
provide parenteral administration of insoluble drugs.
DESIRABLE QUALITIES OF A SUSPENSION
·
Is composed of small uniformly sized particles.
·
Suspended materials must not settle rapidly.
·
Should the particles settle, they must be easily
redistributed. They should not form a hard cake.
·
Should not be too viscous to pour freely from
the orifice of the container or to flow through a syringe needle.
·
For external lotions, suspensions must spread
easily on application, but not too mobile as to run off the surface. The lotion
must dry quickly to give a protective film.
·
Suspensions should have acceptable odour and
taste.
o Should
be resistant to microbial attack (may need a preservative)
o Must
have optimum physical, chemical and pharmacological activities.
PHARMACEUTICAL APPLICATION OF SUSPENSIONS
·
Suspensions provide liquid preparations of
insoluble drugs to patients who find it difficult to swallow tablets and
capsules.
·
To avoid hydrolysis, some drugs are synthesized
as insoluble salts and suspended in a suitable medium. Compare oxytetracycline
hydrochloride (insoluble) and oxytetracycline calcium (soluble).
·
To avoid prolonged contact with liquid, powders
are prepared and suspensions are made just prior to use. E.g. ampicillin syrup
(expires 7-14 days after reconstitution.
·
Provide alternative for aqueous sensitive drugs,
which are suspended in non-aqueous vehicles.
·
Formulation in finely divided particles offer a
high surface area suitable for some drug action e.g. kaolin suspension, Mg
trisilicate and MgCO3 suspensions.
·
Fine powders may provide protective action
against loss of volatile materials for inhalation e.g. Menthol and Eucalyptus
are adsorbed on light Mg carbonate for prolonged release (compared to
solutions).
·
Suspensions may mask an otherwise obnoxious
taste eg. Compare Paracetamol elixir (bitter) and suspension (no taste, can be
sweetened)., or chloramphenicol palmitate is more acceptable in children. Taste
is less noticeable in insoluble form.
·
Topical application may be suitable e.g.
calamine lotion leaves a protective action after the vehicle has evaporated.
·
Parenteral suspensions have controlled release
characteristics (variation in particle size increase duration of action, or
suspension may be formulated in oily phase).
·
Vaccines are often formulated as suspensions and
provide prolonged antigenic stimulus leading to increased antibody titre.
·
Some X-ray contrast media are formulated as
suspension (insoluble materials in aqueous vehicle).
