Emulsions

                                                                    Emulsions

An emulsion is thermodynamically unstable system consists of two immiscible liquids, one of which is dispersed as globules (dispersed phase) in the other liquid phase (the continuous phase).

•The system is stabilized by the presence of an emulsifying agent. •The dispersed liquid or internal phase usually consists of globules of diameters between 0.5 and 25 um, which are distributed within the external or continuous phase.
•The consistency of emulsion system ranged from a mobile liquid to semisolid.

•Types of emulsion;

1-Water in oil w/o

(water globules dispersed in oil phase)

2-Oil in water o /w :

(oil droplets dispersed in water)

3-Multiple emulsion w /o /w or o/w/o

4-Micro emulsion;the dispersed globules (1 nm to 0.5 um diameter), the preparation, is transparent.

•Phase-volume ratio:

is the volume of the internal phase compared with that of the external phase. The most stable emulsions have an internal phase occupying between 40 to 60 % and not more than 74% of the total volume of an emulsion.

Pharmaceutical applications of emulsions:

Emulsions have a wide range of uses, including:

1. Oral emulsions (o/w emulsion);

nTo enhance palatability
nTo increase absorption of oils and oil-soluble drugs through intestinal walls. E.g., griseofulvin suspended in oil in an o/w emulsion.
2. Intramuscular injections (w/o emulsion)
ne.g., water-soluble vaccines to provide slow release and therefore a greater antibody response and longer-lasting immunity (depot therapy) .
3. Intravenousinjections (o / w emulsifier).
nemulsions are used to deliver oily nutrients intravenously to patients, using non-toxic emulsifying agents, such as lecithin
nOnly a few emulsifying agents, E.g. lecithin, gelatin, serum albumin, methyl cellulose and polysorbate 80 (Tween 80) are used for I.V o/w emulsions.

nThe globule size must be kept below 1um to avoid the formation of emboli.

4. Topical application

Emulsions for external use are o/w or w/o,

nThe o / w emulsions are less greasy, easily washed off the skin and more cosmetically acceptable than w/o emulsions.
nThe w/o emulsions, have an emollient effect, which hydrates upper layers of skin.

Emulsifying agents:

•If the emulsifying agent is more soluble in water i.e. Hydrophilic, then water will be the continuous phase and an o/w emulsion will be formed. If the emulsifying agent is more soluble in oil, i.e. lipophilic, then oil will be the continuous phase and a w/o emulsion will be formed.
•The o/w emulsion requires hydrophilic emulsifiers with HLB 8 -18.
•The w/o emulsion requires lipophilic Emulsifiers with HLB 3 -6.
A-o/w emulsifying agents:

1-Monovalent soaps such as sodium oleate. it has HLB value of 18

2-Polyoxyethylene sorbitan mono-oleate (polysorbate 80 or Tween 80). It is hydrophilic nonionic surface-active agent has HLB value of 15.

3-Acacia (salts of d-glucuronic acid).It is hydrophilic colloid has HLB value of 8.

4-Tragacanth (polysaccharide).It has HLB value of 13.2.

5-gelatin (polypeptide and amino acids). It is hydrophilic colloid with HLB value of 9.8

6-Triethanolamineoleate .It is anionic surface active agent has HLB value of 12.

7-lecithin (phospholipid). It is the chief emulsifier In egg yolk.

8-Bentonite (hydrated aluminum silicate). It is solid particles.
B-w/o emulsifying agent:

1-Polyvalent soaps such as calcium plamitate. .

2-Span 80. It is lipophilic nonionic surface active agent has HLB value of 4.3.

3-Cholesterol.

4-Woolfat.