Abstract

DOUBLE EMULSIONS - A REVIEW WITH EMPHASIS ON UPDATED STABILITY ENHANCEMENT PERSPECTIVE

Arka Bhattacharjee*, Arpan Chakraborty and Goutam Mukhopadhyay

ABSTRACT

Water-in-oil-in-water double emulsion, is a colloidal system, generally in which a primary water-in-oil emulsion formed using lipophilic surfactants is dispersed in an aqueous phase with the help of a hydrophilic surfactant. Double emulsions are reported to have good potentials in augmentation of oral bioavailability of drugs having high solubility but low permeability, they also serve as good controlled release drug delivery systems, but their thermodynamic instability problem has limited their industrial applications. Their thermodynamic instability can be attributed to their huge interfacial area resulting in ostwald ripening. For producing these emulsions, primary surfactants with HLB value 2–8, and secondary surfactants with HLB value 6–16 are used. The swelling capacity of the oil globule gets increased on increasing the percentage of lipophilic surfactants whereas with excess of hydrophilic surfactant higher release of internal hydrophilic contents may be observed. Inclusion of electrolyte in inner aqueous phase, gelling of internal or external aqueous phase, thickening of oil layer are helpful in terms of stability enhancement. Regarding formulation aspects to form stable w/o/w emulsions, the emulsions can be incorporated in films by utilizing water vapour impermeable film-formers. Spray drying phenomenon can be utilized to form microspheres which yield emulsions on reconstitution. Adsorption of w/o/w emulsions on solid support enhances stability besides providing facilities of solid dosage form handling. Lastly, self double emulsifying system a recent approach formed by excluding the external aqueous phase, develops into double emulsion in gastric environment, is reported to have enhanced stability aspects.

Keywords: Double emulsions, Lipophilic surfactants, Hydrophilic surfactants, Ingredients of multiple emulsions.