Topical Gel: A Novel approach for drug delivery - Journal of ...

Formulation...Sudhir Bharadwaj et al.include skin studies. Deep tissue penetration can be related to solute protein binding, solute molecularsize and dermal blood flow 12 .Fig. 1 Schematic of Skin Absorption1.2.1. Principles of Topical PermeationBefore a topically applied drug can act either locally or systemically, it must penetrate the stratumcorneum - the skin permeation barrier. Percutaneous absorption involves passive diffusion of substancesthrough the skin. The mechanism of permeation can involve passage through the epidermis itself(transepidermal absorption) or diffusion through shunts, particularly those offered by the relativelywidely distributed hair follicles and eccrine glands (transfollicular or shunt pathway). In the initialtransient diffusion stage, drug molecules may penetrate the skin along the hair follicles or sweat ductsand then absorbed through the follicular epithelium and the sebaceous glands. When a steady state hasbeen reached the diffusion through the intact stratum corneum becomes the primary pathway for topicalpermeation 13 .The release of a therapeutic agent from a formulation applied to the skin surface and its transport to thesystemic circulation is a multistep process, which involves• Dissolution within and release from the formulation• Partitioning into the skin’s outermost layer, the stratum corneum (SC)• Diffusion through the stratum corneum, principally via a lipidic intercellular pathway, (i.e., the ratelimitingstep for most compounds)• Partitioning from the stratum corneum into the aqueous viable epidermis, diffusion through theviable epidermis and into the upper dermis, and uptake into the papillary dermis and into themicrocirculation.1.2.2. Kinetics of Topical Permeation 14-16Knowledge of skin permeation kinetics is vital to the successful development of topical systems. Topicalpermeation of a drug involves the following steps :a. Sorption by stratum corneumb. Penetration of drug through viable epidermis861 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867