RECENT ADVANCES ON TRANSDERMAL DRUG DELIVERY SYSTEM

Transdermal drug delivery is defined as self contained, discrete dosage forms which, when applied to the intact skin, deliver the drug, through the skin at controlled rate to the systemic circulation. There are two important layers of the skin: the dermis and epidermis. The outermost layer is approximately 100 to 150 micrometers thick and thin layer has no blood flow and includes a layer within it known as stratum corneum. This is the layer which is most important for transdermal drug delivery as its composition allows it to keep water within the body and foreign substances out. Beneath the epidermis, the dermis contains a system of capillaries that transport blood throughout the body. If the drug passes the stratum corneum layer then it can enter the blood stream. This process called passive diffusion. Lipid soluble substances readily pass through the intercellular lipid bi layers of the cell membrane whereas water soluble drugs are able to pass through the skin because of hydrated intracellular proteins. Using drug in this manner much more rapid and useful drug delivery is possible.