Recent Advances in Transdermal Drug Delivery System

Human skin serves a protective function by imposing physicochemical limitations. For a drug to be delivered passively via the skin it needs to have a suitable lipophilicity and a molecular weight < 500 Da. The number of commercially available products based on transdermal or dermal delivery has been limited by these requirements. In recent years various passive and active strategies have emerged to optimize delivery. The passive approach entails the optimization of formulation or drug carrying vehicle to increase skin permeability. However, passive methods do not greatly improve the permeation of drugs with molecular weights >500 Da. In contrast, active methods, normally involving physical or mechanical methods of enhancing delivery, have been shown to be generally superior. The delivery of drugs of differing lipophilicity and molecular weight, including proteins, peptides and oligonucletides, has been shown to be improved by active methods such as iontophoresis, electroporation, mechanical perturbation and other energy-related techniques such as ultrasound and needleless injection.