ABSTRACT
Interaction of exogenous molecules with human skin has evoked continuous interest in the scientific community. The concept of topical drug administration on human skin has been prevalent since the rise of early human civilization. In the recent past, however, this concept has been extended beyond delivery of medicaments to localized skin areas. Human skin is now viewed as an interface for systemic delivery of therapeutic molecules. This route, the transdermal drug delivery route, offers several advantages compared to conventional modes of drug delivery such as needles and oral drug delivery. Transdermal delivery offers painless and sustained administration of systemic therapeutics while eliminating first-pass hepatic metabolism and gastrointestinal degradation commonly associated with oral administration. The skin, which has evolved as a natural protective barrier of an organism, strictly regulates the transport of molecules in and out of the body. It is not surprising that most candidate therapeutics find it difficult to overcome this natural barrier to transport. Several physical and chemical methods have been studied to perturb or compromise the skin barrier to promote the flux of therapeutics into or across the skin (1-5). The prime requirements of any such technique should be: sufficient barrier disruption for optimal flux and quick reversibility of physiological functions at the site of disruption after termination of the treatment. Iontophoresis (6-15), sonophoresis (16-24), electroporation (25-31), and microneedles (32-37) are some of the physical techniques used to compromise the barrier function of skin. Chemical penetration enhancers (CPEs) (38-47), liposomes (48-52), ethosomes (53-55), transferosomes (56,57), niosomes (58,59), and emulsions (60-63) are some of the chemical methods used for enhancing transdermal drug delivery.
