Abstract: Skin serves as a barrier against local and systemic effects and is one of the largest organs. The outermost layer of the skin, the Stratum Corneum (SC), is impermeable to hydrophilic and high molecular weight drugs. Drugs can infiltrate deeper layers of the skin's blood circulation through ethosomes without requiring surgical intervention. As new vesicular carriers for the transfer of active compounds to/through the skin, "smooth vesicles" known as ethosomes function. Most of them are made up of phospholipids, water, and ethanol (phosphatidylcholine, phosphatidylserine, and phosphatidic acid). Ethosomes can serve as a capsule for the release and transportation of both hydrophilic and lipophilic medications via the skin because of their amphiphilic properties. Comparing other vesicles that serve as drug delivery systems, ethanol is present in ethanolosomes at a rate of 45 percent, which is the greatest concentration. Ethosomes are liposomes that are heavily ethanolcontained. Tens of nanometers to microns are the sizes of ethosomes. By piercing the dermal layers of the skin, they can transfer drugs to the deep skin or systemic circulation.

Abstract Topical administration of drugs is delivering medications locally to the eye, skin, rectum and vagina. This route of drug application has many advantages including bypassing the extensive hepatic metabolism, avoiding the invasive parenteral (injection) and others. Emulgel is a semisolid preparation which has advantages of having a high ability to skin penetration than other semisolid formulations, being greaseless, thixotropic, easily spreadable and removable, water soluble, non-staining, emollient and longer half-life. There are many ingredients and constituents of emulgel such as oils, emulsifying agents and gelling agents. Emulgel is prepared as either o/w or w/o type. Many evaluations had been performed to check the properties of emulgel such as organoleptic properties, spreadability, pH, viscosity, rheological study, swelling index, Ex-vivo bioadhesive strength measurement of topical emulgel and others

Abstract Letrozole (LZL) is a non-steroidal competitive aromatase enzyme system inhibitor. The aim of this study is to improve the permeation of LZL through the skin by preparing as nanoemulsion using various numbers of oils, surfactants and co-surfactant with deionized water. Based on solubility studies, mixtures of oleic acid oil and tween 80/ transcutol p as surfactant/co-surfactant (Smix) in different percentages were used to prepare nanoemulsions (NS). Therefore, 9 formulae of (o/w) LZL NS were formulated, then pseudo-ternary phase diagram was used as a useful tool to evaluate the NS domain at Smix ratios: 1:1, 2:1 and 3:1. All the prepared formulae were characterized for thermodynamic stability studies, zeta potential, droplet size, polydispersity index (PDI), % transmittance estimation, pH, % drug content, electro-conductivity and in vitro drug release. NS-7 (compose of 5% oleic acid, 45% Smix of 1:9 ratio and 50% water) was chosen as an optimum prepared formula for many reasons. Initially, it has a lower PDI (0.054), optimum droplet size (75.9 nm), highest transmittance percent (99.89±0.015%), high drug content (99.88%±0.03%), acceptable pH (5.96±0.025), highest electro-conductivity (230±1 μS/cm) and optimum drug release% (99.58±1.92) after 75 min in phosphate buffer (pH 6.8) compared to other NS formulations.One can conclude that preparation of LZL NS is an effective method for improving the permeation of LZL throught the skin. Keywords: Letrozole, Nanoemulaion, Permeation and in vitro release