ABSTRACT:
Transdermal drug delivery system (TDDS) provides various merits over conventional drug delivery systems such as oral delivery and injections including avoidance of hepatic first pass metabolism, reduction of pain, and possible sustained release of drug. Still, transdermal passage of molecule is tedious due to less permeability of stratum corneum (SC), the outermost layer of the skin. In its intact state the skin is a formidable barrier, resistant to chemicals and tissue-harmful ultraviolet rays and virtually impenetrable to the life threatening microorganisms. The stratum corneum (SC) develops a thin, tough, relatively impermeable membrane which usually provides the rate limiting step in transdermal drug delivery system. To overcome this barrier function chemical permeation enhancers (CPEs) are used that facilitate the absorption of permeate through the skin by temporarily decreasing the impermeability of the skin. The present review article highlights the different layer of skin and the passage of drug through a transdermal patch into the stratum corneum for local or systematic effect.