Abstract
Transdermal drug delivery systems (TDDS) offer several advantages over other administration routes. Clinically, several drugs, e. g. nitroglycerin and tulobuterol etc., have been used successfully in TDDS. However only a limited number of drugs can penetrate the skin sufficiently due to the inherent function of the skin which is to exclude external chemicals. In order for broader classes of drugs to be successfully delivered across the skin, the technology of percutaneous penetration enhancement, both in the form of chemical entities and physical methods has been the subject of research. Although some chemical enhancers or enhancement formulations have been used in TDDS, their potential may not be sufficient for rnacromolecular medicine as used in injection. Therefore, a physical enhancement method provide more potential to deliver drugs though the skin more powerfully and precisely. In this review, we focus on the physical enhancement approach as we believe it is the key to the future development of TDDS. In particular, iontophoresis and sonophoresis technologies are overviewed for their principle mechanisms, characteristics and the present situation of their development. Other physical enhancement approaches, like microneedles and electroporation etc. are also explained briefly.
