Transdermal drug delivery system offers an alternative pathway for systemic drug delivery with several advantages over conventional routes. Unfortunately, the barrier nature of the skin presents a significant obstacle for most drugs to be delivered. Consequently, several approaches including both the chemical and physical enhancement strategies are used to increase skin permeability. Potential substances used for this purpose need to have both features, i.e. drug penetration-promoting effects and a low or no skin irritating potential. However, none of the chemical penetration enhancer...