Multiple emulsions and its stabilization: A review
Navneet Kumar Verma, Jai Narayan Mishra
Multiple emulsions are also known as emulsions of emulsions, liquid membrane system or double emulsion. These have been proposed to have numerous uses including their use for enhancement of bioavailability or as a prolonged drug delivery system. Multiple emulsions are often stabilized using a combination of hydrophilic and hydrophobic surfactants. The ratio of these surfactants is important in achieving stable multiple emulsions. The two major types of multiple emulsions are the w/o/w and o/w/o emulsions. Multiple emulsions are multifarious polydispersed systems where both oil in water and water in oil emulsion exists all together which are stabilized by lipophillic and hydrophilic surfactants respectively. The ratio of these surfactants is important in achieving stable multiple emulsions. Among water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) type multiple emulsions; the former has wider areas of application. Formulation, preparation techniques and in vitro characterization methods for multiple emulsions are reviewed. It finds wide range of applications in controlled or sustained drug delivery, targeted delivery, taste masking, bioavailability enhancement, enzyme immobilization, etc. Multiple emulsions have also been employed as intermediate step in the microencapsulation process and are the systems of increasing interest for the oral delivery of hydrophilic drugs, which are unstable in gastrointestinal tract like proteins and peptides.