Abstract : Topical formulation are the products which are administered by applying over the surface of the skin intended to deliver the API onto/or across the skin or mucous membrane in order to achieve pharmacological or cosmetic like effect by local action and/or systemic action, in the form of solid, liquid, and semisolid dosage form. It is a painless method for the delivery of drugs systematically by applying a drug on to intact and healthy skin. The drug penetrates through the stratum corneum and after that passes through the deeper epidermis and dermis without any accumulation of drug in the dermal layer. When drug reaches to the dermal layer of skin, it becomes for systemic absorption via the dermal microcirculation. For the development of successful TDDS system, it is important to understand the kinetics of skin permeation. For the evaluation of TDD, the assessment of percutaneous absorption of molecules is very Important step. Percutaneous absorption includes the penetration of drug into the various layers of skin8 and permeation across the skin into the systemic circulation.
