emulsion

EmulsionEmulsion

An emulsion is essentially a An emulsion is essentially a liquidliquid

preparation containing a preparation containing a mixturemixture

of oil and water that is of oil and water that is renderedrendered

homogeneous by the additionhomogeneous by the addition

of an emulsifying agent.of an emulsifying agent.

British Pharmacopoeia British Pharmacopoeia (BP) (BP) Definition (oral emulsions)Definition (oral emulsions)

• Oral emulsions are oral liquids Oral emulsions are oral liquids containing one or more active containing one or more active ingredients. They are stabilised oil-in-ingredients. They are stabilised oil-in-water dispersions, either or both water dispersions, either or both phases of which may contain phases of which may contain dissolved solids.dissolved solids.

Advantages and disadvantagesAdvantages and disadvantagesof emulsions as dosage formsof emulsions as dosage forms

AdvantagesAdvantages• Unpalatable oils can be administered in palatable Unpalatable oils can be administered in palatable

form.form.• Unpalatable oil-soluble drugs can be Unpalatable oil-soluble drugs can be

administered inadministered in• palatable form.palatable form.• The aqueous phase is easily flavoured.The aqueous phase is easily flavoured.• The oily sensation is easily removed.The oily sensation is easily removed.• The rate of absorption is increased.The rate of absorption is increased.• It is possible to include two incompatible It is possible to include two incompatible

ingredients, one in each phase of the emulsion.ingredients, one in each phase of the emulsion.

DisadvantagesDisadvantages

• Preparation needs to be shaken well before Preparation needs to be shaken well before use.use.

• A measuring device is needed for A measuring device is needed for administration.administration.

• A degree of technical accuracy is needed A degree of technical accuracy is needed to measure a dose.to measure a dose.

• Storage conditions may affect stability.Storage conditions may affect stability.• Bulky, difficult to transport and prone to Bulky, difficult to transport and prone to

container breakages.container breakages.• Liable to microbial contamination which Liable to microbial contamination which

can lead to cracking.can lead to cracking.

Extemporaneous preparationExtemporaneous preparation

In oral emulsions prepared according to In oral emulsions prepared according to the formula and directions given for the formula and directions given for extemporaneous preparation, the quantityextemporaneous preparation, the quantity

of emulsifying agent specified in of emulsifying agent specified in individualindividual

monographs may be reduced to yield a monographs may be reduced to yield a preparation of suitable consistencypreparation of suitable consistency

provided that by so doing the stability of provided that by so doing the stability of the preparation is not adversely affected.the preparation is not adversely affected.

Stability of emulsionsStability of emulsions

Emulsions can break down in the Emulsions can break down in the followingfollowing

ways:ways:

• crackingcracking

• creamingcreaming

• phase inversion.phase inversion.

CrackingCracking

• This is the term applied when the disperseThis is the term applied when the disperse

phase coalesces and forms a separate layer.phase coalesces and forms a separate layer.

Redispersion cannot be achieved by shakingRedispersion cannot be achieved by shaking

and the preparation is no longer an emulsion.and the preparation is no longer an emulsion.

Cracking can occur if the oil turns rancidCracking can occur if the oil turns rancid

during storage. The acid formed denatures during storage. The acid formed denatures the emulsifying agent, causing the two phases the emulsifying agent, causing the two phases toto

separate.separate.

CreamingCreaming

In creaming, the oil separates out, In creaming, the oil separates out, forming a layer on top of the forming a layer on top of the emulsion, but it usually remains in emulsion, but it usually remains in globules so that it can be redispersed globules so that it can be redispersed on shaking (e.g. the cream on the on shaking (e.g. the cream on the top of a pint of milk). top of a pint of milk).

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This is undesirable as the product This is undesirable as the product appearance is poor and if the product appearance is poor and if the product is not adequately shaken there is a is not adequately shaken there is a risk of the patient obtaining an risk of the patient obtaining an incorrect dose. Creaming is less incorrect dose. Creaming is less likely to occur if the viscosity of the likely to occur if the viscosity of the continuous phase is increased.continuous phase is increased.

Phase inversionPhase inversion

This is the process when an oil-in-This is the process when an oil-in-water emulsion changes to a water-water emulsion changes to a water-in-oil emulsion or vice versa. For in-oil emulsion or vice versa. For stability of an emulsion, the optimum stability of an emulsion, the optimum range of concentration of dispersed range of concentration of dispersed phase isphase is

30–60% of the total volume.30–60% of the total volume.


If the disperse phase exceeds this, If the disperse phase exceeds this, the stability of the emulsion is the stability of the emulsion is questionable. As the concentration of questionable. As the concentration of the disperse phase approaches a the disperse phase approaches a theoretical maximum of 74% of the theoretical maximum of 74% of the total volume, phase inversion is more total volume, phase inversion is more likely to occur.likely to occur.

Summary of the problemsSummary of the problemsencountered by emulsionsencountered by emulsions

•Creaming:Creaming: Separation of the emulsion intoSeparation of the emulsion into two regions, one containing more of the two regions, one containing more of the

disperse phase.disperse phase.Possible reasons for problem:Possible reasons for problem:• lack of stability of the system.lack of stability of the system.• product not homogeneous.product not homogeneous.Can be saved emulsion on shaking.Can be saved emulsion on shaking.

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Cracking:Cracking: The globules of the disperse phaseThe globules of the disperse phasecoalesce and there is separation of the coalesce and there is separation of the

disperse phase into a separate layer.disperse phase into a separate layer.Possible reasons for problem:Possible reasons for problem:• incompatible emulsifying agentincompatible emulsifying agent• decomposition of the emulsifying agentdecomposition of the emulsifying agent• change of storage temperature.change of storage temperature.The emulsion will not reform on shaking.The emulsion will not reform on shaking.


Phase inversionPhase inversion

From oil-in-water to water-in-oil orFrom oil-in-water to water-in-oil or

from water-in-oil to oil-in-water.from water-in-oil to oil-in-water.

Possible reason for problem:Possible reason for problem:

• amount of disperse phaseamount of disperse phase

• greater than 74%.greater than 74%.

The emulsion will not reform on shaking.The emulsion will not reform on shaking.

emulsion

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