Chemical Penetration Enhancers for Transdermal Drug Delivery - Success and Challenges

Chemical penetration enhancers (CPEs), which are also referred to as sorption promoters or accelerants have several advantages in transdermal drug delivery. These are painlessness, noninvasiveness and the capacity to increase in transdermal flux in comparison with passive diffusion. Several investigators have used a number of chemical enhancers to demonstrate these important properties. Studies have also been carried out to have a better understanding of the mechanisms of penetration enhancement. It has been postulated that these compounds can enhance transdermal drug delivery by perturbing the stratum corneum, increasing partition coefficient or increasing solubility. In this paper, several compounds used in facilitating percutaneous penetration of drugs have been described and the potential of using them for transdermal drug delivery highlighted. Special attention has been paid to cell-penetrating proteins (protein transduction domains) as well as skin penetrating peptides. Ironically, these are substances that possess high molecular weight themselves but are capable of creating pores through which drugs can penetrate into and through the skin. Concerns relating to irritation and cytotoxicity and efforts to overcome them are discussed.