ABSTRACT
Although several drugs are now available on the market as transdermal patches, none of these is a peptide or protein drug. The reasons are not difcult to guess. The skin is ordinarily permeable only to small lipophilic molecules, a criterion readily fullled by drugs such as nitroglycerin, scopolamine, clonidine, nicotine, and other drugs on the market. Peptide and protein drugs, being hydrophilic and macromolecular in nature, do not readily permeate the skin. However, recently some enhancement techniques such as iontophoresis are becoming available, which are likely to make transdermal delivery a promising approach for delivery of peptide/protein and other biotechnology-derived drugs (Kasha & Banga, 2008; Nolen, Catz, & Friend, 1994; Panchagnula, Pillai, Nair, & Ramarao, 2000; Pillai, Nair, Poduri, & Panchagnula, 1999; Wallace & Lasker, 1993). Other promising enhancement techniques include use of ultrasound energy (phonophoresis) and creation of microscopic holes (microporation) by microneedles or other thermal means (Banga, 2011; Schoellhammer, Blankschtein, & Langer, 2014).
