The effects of emulsifiers and emulsion formulation types on dermal and transdermal drug delivery

Abstract

Emulsions are widely used in the cosmetic and pharmaceutical fields for the topical administration of hydrophilic and lipophilic active ingredients. There exist different types of emulsions, e.g. water-in-oil, oil-in-water, water-in-oil-in-water and oil-in-water-in-oil. Furthermore, emulsions are thermodynamically unstable and necessitate an emulsifier for the formation and stabilisation. Both, the type of emulsion and emulsifier could affect dermal and transdermal delivery, which has been reviewed in this chapter. Due to the complexity of topical emulsions and consequently the difficulty to investigate the exclusive effect of emulsifiers and emulsion type on skin absorption, as other emulsion ingredients may also contribute to interactions with the active ingredient and the skin, this chapter aimed at focusing mainly on studies with a systematic approach. For example, studies were included that investigated emulsions with the same composition and only differed in the emulsifier component or emulsion type. The review demonstrated that the type of emulsion significantly affected the dermal and transdermal delivery. In general, skin penetration of hydrophilic active ingredients was enhanced when the active was incorporated into the continuous phase of the emulsion. Furthermore, multiple o/w/o emulsions, in comparison to simple w/o emulsions, reduced the transdermal delivery of lipophilic active ingredients, whereas the dermal delivery was increased. Therefore, multiple emulsions could be useful for prolonged topical delivery. It was also demonstrated that the effect of the emulsifiers on dermal and transdermal delivery could vary, depending on the structure and physicochemical properties of the emulsifier/emulsifier system, such as the hydrophilic chain length, hydrophilic-lipophilic balance (HLB) value, emulsifier charge or solid particles vs. surfactant