17-06-2013, 02:02 PM
Pharmaceutical Formulation Technology
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Definition:
Emulsion is thermodynamically unstable system consisting of at least two immiscible liquid phases one of which is dispersed as globules (the dispersed phase) in the other liquid phase (the continuous phase/ external phase) stabilized by presence of emulsifying agent.
Pharmaceutical Emulsions:
1) Lotions
2) Liniments
3) Creams
4) Ointments
5) Vitamin drops
Types of Emulsions with respect to particle size of dispersed phase Microemulsion:
Droplets size range 0.01 to 0.1 m m Microemulsions are clear, stable, liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. In contrast to ordinary emulsion, microemulsions form upon simple mixing of the components and do not require the high shear conditions generally used in the formation of ordinary emulsions.
Topical
Oils used as emollients or protectants of skin, when emulsified they feel less greasy Enhanced transdermal absorption
Composition of an Emulsion
Internal/Discontinuous/Dispersed phase External/Continuous phase/Dispersing medium Emulsifying agent
Choice of Emulsion Types
• Fats or oils for oral administration: - o/w is formed to mask unpleasant taste
• For i.v. administration: o/w and w/o
• For external application: o/w for water soluble drugs, easily washable from skin and has non greasy texture w/o occlusive effect influence the absorption of drugs and cleansing skin, moisturizing creams (designed to prevent moisture loss from skin)
Bancroft's rule:
Emulsion type depends more on the nature of the emulsifying agent than on the relative proportions of oil or water present or the methodology of preparing emulsion.The phase in which an emulsifier is more soluble constitutes the continuous phase In O/W emulsions – emulsifying agents are more soluble in water than in oil (High HLB surfactants). In W/O emulsions – emulsifying agents are more soluble in oil than in water (Low HLB surfactants). Bancroft states that the necessary conditions for forming a stable emulsion are that the drops of the dispersed phase shall be so small that they will stay suspended and that there shall be a sufficiently viscous film around each drop to keep the drops of the dispersed phase from coalescing.