Suspensions

34


Suspensions




Study Points



image The nature of suspensions


image The pharmaceutical uses of suspensions


image The properties of an ideal suspension


image Formulating a suspension


image Ingredients which may be added to suspensions


image The dispensing of suspensions for internal and external use



Introduction


Suspensions contain one or more insoluble medicaments in a vehicle, with other additives such as preservatives, flavours, colours, buffers and stabilizers. Most pharmaceutical suspensions are aqueous, but an oily vehicle is sometimes used. Suspensions may be used for oral administration, inhalation, topical application, as ophthalmic preparations, for parenteral administration and as aerosols.


A pharmaceutical suspension may be defined as a disperse system in which one substance (the disperse phase) is distributed in particulate form throughout another (the continuous phase). Most are classified as a coarse suspension, which is a dispersion of particles with a mean diameter>1 μm. A colloidal suspension is a dispersion of particles with a mean diameter<1 μm. Suspended solids slowly separate on standing, but redispersion may be difficult if they form a compacted sediment.



Pharmaceutical applications of suspensions


Suspensions may be used pharmaceutically for a number of reasons. Some are given below:



image Drugs with low solubility in the continuous phase can be formulated as suspensions


image Patient acceptability – a liquid form rather than a solid dosage form


image Drugs that have an unpleasant taste in their soluble form can be made into insoluble derivatives, and formulated as a suspension, which will be more palatable, e.g. chloramphenicol (soluble) and chloramphenicol palmitate (insoluble)


image In oral suspensions, the drug is delivered in finely divided form, therefore optimal dissolution occurs in the gastrointestinal (GI) fluids and hence the rate of absorption is increased


image Insoluble forms of drugs may prolong the action of a drug by preventing rapid degradation in the continuous phase


image If the drug is unstable when in contact with the vehicle, suspensions should be prepared immediately prior to handing out to the patient in order to reduce the amount of time that the drug particles are in contact with the dispersion medium. For example, in ampicillin suspension, water is added to powder or granules prior to giving out to the patient. A 14-day expiry date is given, if the product is to be kept in the fridge


image Drugs which degrade in aqueous solution may be suspended in a non-aqueous phase, e.g. tetracycline hydrochloride has been suspended in a fractionated coconut oil for ophthalmic use


image Bulky, insoluble powders can be formulated as a suspension so that they are easier to take, e.g. kaolin, chalk and magnesium trisilicate (see Examples 34.1 and 34.2)



Example 34.2


Prepare 100 mL of Chalk Mixture, Paediatric BP.
































  Master formula For 100 mL
Chalk 100 mg 2 g
Tragacanth 10 mg 200 mg
Syrup 0.5 mL 10 mL
Concentrated cinnamon water 0.02 mL 0.4 mL
Double strength chloroform water 2.5 mL 50 mL
Water to 5 mL to 100 mL


Example 34.1


Prepare 150 mL Kaolin and Morphine Mixture BP.
























  Master formula For 150 mL
Light kaolin 2 g 30 g
Sodium bicarbonate 500 mg 7.5 g
Chloroform and morphine tincture 0.4 mL 6 mL
Water to 10 mL to 150 mL

image Intramuscular, intra-articular or subcutaneous injections are often formulated as suspensions to prolong the release of the drug


image Lotions containing insoluble solids are formulated to leave a thin coating of medicament on the skin. As the vehicle evaporates, it gives a cooling effect and leaves the solid behind. Examples are Calamine Lotion BP (see Example 34.3) and Sulphur Lotion Compound BPC (see Ch. 36).



Example 34.3


Prepare 200 mL Calamine Lotion BP.




































  Master formula For 200 mL
Calamine 15 g 30 g
Zinc oxide 5 g 10 g
Bentonite 3 g 6 g
Sodium citrate 500 mg 1 g
Liquefied phenol 0.5 mL 1 mL
Glycerol 5 mL 10 mL
Water to 100 mL to 200 mL

Related posts:

  1. Oral unit dosage forms
  2. Pharmaceutical calculations
  3. Public health
  4. Emulsions

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Jun 24, 2016 | Posted by in PHARMACY | Comments Off on Suspensions

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