Magoosh GRE

What is the Preparation and Stability of Calamine Suspension?

| December 11, 2012

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Suspensions are solid dipersion of insoluble or sparingly-soluble drugs, in aqueous like keltrol or oily vehicles such as emulsion. Suspension are used for oral administration, external application to the skin (topical) or parenteral administration.These  particles suspended into liquid medium do not  dissolve but have dispersed in according to the particles size, and can settle to form to layer (drug layer/fluid medium) due to gravity(sedimentation). Due to this reason Suspension agents are used to redistribute the suspension on shaking. In order for a drug to have impact the solid particles should not be greater than micrometers to aid in dispersion and absorption within the body and to avoid in creams a gritty effect.   In this experiment we looked at calamine lotion suspension in which sodium citrate (preservative) and betonies are the suspension agents. (1,2)


7.5g of calamine and 2,5g of zinc oxide was weighed and grinded in a pestle and mortar to a fine powder, 2.5ml of glycerin was added to this power mixture and grinded to a fine mixture which took roughly 2-5 minutes. The remaining residues of the glycerin within the cylinder were washed out with 6 5ml portions of water. This was transferred into a 50ml cylinder with the slurry from the mortar and made to bulk (50ml) with water. Clingfilm was used to wrap the top of the cylinder to prevent leaks while gently inverting the cylinder repeatedly until the product was homogenous. This was then placed on the bench and timer was started to record the volume of sediment and overall volume in ml. Results were tabulated.


The results ands graph show that  formula D sedimentation was the most rapid followed by formulae A It would have been expected that formula A would have the highest sedimentation rate due there not being any bentonite and sodium citrate present. Formula D is result is accurate this is due to errors. Comparing Formula B and I as both had 1.5g of one Flocculants  in mixture, formula B which only contained bentonite, the sedimentation rate was slightly faster. Formula F which contained both, but bentonite is excess, this mixture had the slowest sedimentation rate A combination of the two flocculants shows to be the most effective



From the experiment we were able to achieve fairly good results, the results showed that bentonite and sodium citrate played a key role in the rate of sedimentation as it provided and maintained the viscosity of the suspension and the uniformity. Also we can also conclude that bentonite is also more effective that sodium citrate as a suspension agent.



(1) date:14/03/11

(2) date 14/03/11

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