Microemulsions as Platforms for Transdermal Delivery of Hydrophilic Drugs - A Review

Background: Delivery rates in cutaneous applications are limited by the skin barrier and also by the physical-chemical properties of the drug in the formulation. A lipophilic drug has more affinity, and can permeate the epidermis more easily than a hydrophilic drug. The potential use of nano-sized dispersions as distribution systems for hydrophilic drugs is being investigated. Objective: To analyze the literature with regard to the development of microemulsions (ME) for transdermal delivery of hydrophilic drugs, with a view to identifying strategies to increase the permeation of these drugs. Results: One hundred and eleven articles were potentially relevant to the combination of search criteria. After excluding duplicated articles, the abstracts of 83 articles were read. Of these, 73 did not meet the inclusion criteria. To complete the review process, the whole text of 10 articles was evaluated. Conclusion: The main factors that positively influenced the permeation of hydrophilic drugs were low hydrophilic-lipophilic balance (HLB) values of the surfactant; concentrations of about 40% of surfactants and 30% of aqueous phase for the water-in-oil (W/O) systems; the addition of permeation promoters to the systems; and the association of physical methods during the application of the ME. The results offered support for the development of new topical microemulsions for hydrophilic drug delivery.