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Microemulsion (ME) systems are now considered of the most successful transdermal drug delivery systems. This is due to their nanodroplets size in the one hand and to their composition that enables the use of several mechanistically penetration enhancers in the same formulation on the other hand. This work summarizes the types, properties, and the merits of the use of MEs for transdermal delivery and reviews the successful studies that were performed to deliver several drugs through this important route during the past 10–12 years.

The main focus of the current work was to design, evaluate and clinically compare the efficiency of novel metronidazole (MTD) loaded solid lipid nanoparticles (SLNs) vaginal emulgel with the marketed vaginal gel (Metron®) against Bacterial vaginosis (BV). Eight formulations were fabricated using 23 full factorial design and prepared by stearic acid and tween 80 as solid lipid and surfactant, respectively. Lipid and surfactant concentrations in addition to sonication amplitude were chosen as the independent variables (X1–X3). Then, the prepared MTD loaded SLNs were evaluated based on the dependent variables which were particle size, polydispersity index, zeta potential, entrapment efficiency, and cumulative % drug release for 24 h (Y1–Y5). The in vitro release study exhibited a sustained release of MTD from the SLNs up to 24 h. The optimal MTD loaded SLNs showed nanosized particles (256 nm) with EE% (52%), and an acceptable ZP value (−29.5 mV). Also, the optimized MTD-SLNs formulation was incorporated into Carbopol emulgel and investigated clinically for its effect against BV. Clinical studies recorded significant enhancement in therapeutic response of MTD from optimized SLNs vaginal emulgel formulation regarding the clinical treatment (p

Targeting solid tumors transdermally is an emerging approach that is currently under intense investigation. In this context, microemulsions are reported as one of the most favored carriers for successful transdermal drug delivery. Thereby, these nano-carriers were utilized in this study for the delivery of a phytochemical, namely methyl dihydrojasmonate (MDHJ), which has previously demonstrated an anticancer effect. Accordingly, pseudoternary phase diagrams were constructed using several combinations of oils, surfactants and co-surfactants and following the water titration method. Two systems were selected and an experimental design (Simplex Lattice Mixture Design) was utilized to select formulations for further investigation through an ex vivo permeation study through mouse skin. Transdermal fluxes were determined reaching a value of 0.07μlcm-2h-1. Cytotoxicity studies were carried out where the selected superlative formulation was further investigated on MCF-7 cell lines and scored an IC50 of 42.2μl/ml (equivalent to 8.3μl/ml drug). Further, in vivo investigations were performed using Ehlirch solid carcinoma and histopathological examination of the tumor cells evaluating the tumor volume differences, tumor inhibition percentages and the necrotic effect of the formulation compared to control, placebo and pure drug. The obtained results showed significant anticancer effects of the selected formulation when applied on the tumor bearing mice skin.