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Transdermal drug delivery (TDD) have been proved to be a very useful delivery route for the administration of both locally working chemicals and systemically effective pharmaceuticals. There are various advantages of TDD over oral delivery, including improved bioavailability due to the avoidance of first-pass effect and the gastrointestinal degradation, minimized side effects by circumvention of direct contact with gastrointestinal tract and increased patient compliance due to less frequent administration and the less fluctuation in plasma drug concentration. Since the first patch of scopolamine for motion sickness in 1981, TDD has gained significant interest for lipophilic drug molecules with low biological half-life and enormous efforts have been made for the development of transdermal patch products. However, the effort is not satisfactorily reflected in current TDD area, and only about 40 transdermal patch products has been introduced into the market for about 20 drug molecules. Hence, for the breakthrough of this stagnant situation in TDD field, it is extremely important to develop new transdermal penetration enhancing technology and expand the number of applicable drug molecules, including the hydrophilic and macromolecular drug molecules. In this paper, we have reviewed briefly various physical and chemical penetration enhancing technology, and some recent advancements are introduced.
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