Transdermal Drug Delivery Systems Influencing Factors, Study Methods and Therapeutic Applications

Drug delivery across the skin offers several advantages, which includes bypassing of gastrointestinal tract and deviation from liver metabolism. Several drugs have been successfully assimilated through this route, which is in turn controlled by the drug lipophilicities and molecular weights along with their partition coefficients. The age and condition of the skin are also determining factors. However, an obvious barrier to this process is the stratum corneum which restricts efficient penetration of drugs. This drawback has been partially overcome by the use of permeation enhancers, and also by coercive techniques, which promote easy drug uptake, as proved by various in vitro and in vivo assays. Consequently, several transdermal delivery based therapeutic systems have been developed to treat various specific pathological conditions. The factors controlling drug uptake and penetration enhancers have been discussed in this review, along with some important therapeutic applications.