ABSTRACT
The term percutaneous absorption covers the entire process by which a drug applied to the outer surface of the skin is taken up into the systemic circulation. This requires penetration into the layers of the skin with subsequent permeation across each layer and finally uptake into the capillary blood vessels in the upper region of the dermis. It is necessary to consider both the structure of the membrane and the interactions of the three components – membrane, penetrant and vehicle to determine the physical and chemical factors which assist or hinder the process. Not all drug substances are suitable for transdermal delivery. Among the factors playing a part in percutaneous absorption are the physical and chemical properties of the drug, including its molecular weight, solubility, partition coefficient, dissociation constant (pKa), the nature of the carrier vehicle, and the condition of the skin. Although general statements applicable to all possible combinations of drug, vehicle, and skin condition are difficult to draw, most research findings were tried to summarize in this review article.