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 difficult to guess. The skin is ordinarily permeable only to small lipophilic molecules, a criterion readily fulfilled by drugs such as nitroglycerin, scopolamine, clonidine, nicotine, and other drugs on the market. Peptide and protein drugs, because they are hydrophilic and macromolecular, do not readily permeate the skin. However, some enhancement techniques (e.g., iontophoresis) are becoming available and are likely to make transdermal delivery a promising approach for delivery of peptide/protein and other
biotechnology-derived drugs.6-9 Other promising enhancement techniques include use of ultrasound energy (phonophoresis) and creation of microscopic holes (microporation) by microneedles or other thermal means.
