Emulsion

Emulsion  An emulsion is essentially a liquid preparation containing a mixture of oil and water that is rendered homogeneous by the addition of an emulsifying agent.

British  P harmacopo eia  (B P) Def in   itio n (ora l em ulsio ns )  Ora l em ulsio ns  ar e ora l li qui ds  co ntai ni ng o ne or  mor e active i ngr edi ents . Th ey ar e sta bi lis ed oi l-i n-wat er  disp ersio ns, eith er  or  both  phas es  o f which  ma y co ntai n disso lved so li ds .

 Advantages and disad vantages of emulsions as dosage forms       

 Advantages Unpalatable oils can be administered in palatable form. Unpalatable oiloil-soluble drugs can be administered in palatable form. The aqueous phase is easily fla voured. The oily sensation is easily removed. The rate of absorption is increased. It is possible to include two incompatible ingredients, one in each phase of the emulsion.

Disadvantages  Preparation needs to be shaken well before use.   A measuring de vice is needed for    

administration.  A degree of technical accuracy is needed to measure a dose. Storage conditions may affect stability. Bulky, difficult to transport and prone to container breakages. Liable to microbial contamination which can lead to cracking.

Extemporaneous preparation In oral emulsions prepared according to the formula and directions given for extemporaneous preparation, the quantity of emulsifying agent  of  agent specified in individual monographs may be reduced to yield a preparation of  of suitable consistency provided that  that by so doing the stability of  the preparation is not not adversely affected affected..

Stability of emulsions Emulsions can break down in the following ways:  cracking  creaming  phase inversion.

Cracking

 This is the term applied when the disperse phase coalesces and forms a separate layer. Redispersion cannot be achieved by shaking and the preparation is no longer an emulsion. Cracking can occur if the oil turns rancid during storage. The acid formed denatures the emulsifying agent , causing the two phases to separate.

Creaming

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

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

Phase

inversion

This is the process when an oiloil-in in--water emulsion changes to a waterwater -in in--oil emulsion or vice versa. For stability of an emulsion, the optimum range of  concentration of dispersed phase is 30 30  60% 60% of the total volume.

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

Summary of the problems encountered by emulsions

 Creaming: Separation of the emulsion into two regions, one containing more of the disperse phase. Possible reasons for problem:  lack of stability of the system.  product not homogeneous. Can be saved emulsion on shaking.

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Cracking: The globules of the disperse phase coalesce and there is separation of the disperse phase into a separate layer. Possible reasons for proble m :  incom patible em ulsifying agent   decom position of the em ulsifying agent   change of storage tem perature. The em ulsion will not reform  on shaking.

---Continued --Continued----Phase inversion From oiloil-in in--water to waterwater-inin-oil or from waterwater-in in--oil to oiloil-inin-water. Possible reason for p roblem:  amount of disp erse p hase  greater than 74%. The emulsion will not reform on shaking.