Biocompatible topical microemulsions – use and perspectives as cutaneous delivery systems for medicines

Abstract

This review refers to biocompatible microemulsions, which in recent decades have attracted the interest of formulators as nanosystems useful for the skin drug delivery. Microemulsions are homogeneous pseudoternary colloidal dispersions, thermodynamically stable, fluid, transparent, isotropic, consisting of an oil phase and an aqueous phase, stabilized by a mixture of surfactant and cosurfactant and with the droplet diameter of the dispersed phase usually within the range 10-100 nm. To support the potential of biocompatible microemulsions as an innovative topical pharmaceutical form, this paper provides an overview of their type, formulation, structure, composition and characterization, as well as their advantages and disadvantages. Currently, the main purpose of the dermal microemulsion formulation is to obtain optimal drug bioavailability under conditions of minimal skin irritability. Numerous studies carried out in the last two decades have shown the potential of microemulsions to increase the percutaneous penetration of drugs, acting as penetration enhancers due to the following advantageous characteristics: high solubilization capacity of natural and synthetic lipophilic and hydrophilic compounds; the release of a large amount of active ingredient in the skin, followed by an increased dermal distribution and permeation. Ensuring skin tolerance in the presence of large amounts of surfactant and co-surfactant in the formulation of microemulsions can be achieved by selecting clinically accepted excipients for topical preparations and generally recognized as safe (Food and Drug Administration). Therefore, biocompatible dermal microemulsions can be prepared using natural excipients (vegetable oils, non-ionic surfactants, volatile oils), which are biodegradable and have lower skin toxicity and irritant potential than synthetic ones.