In recent years there has been a drive to create experimental techniques that can facilitate the accurate
and precise prediction of transdermal permeation without the use of in vivo studies. This review considers why
permeation data is essential, provides a brief summary as to how skin acts as a natural barrier to permeation and
discusses why in vivo studies are undesirable. This is followed by an in-depth discussion on the extensive range of
alternative methods that have been developed in recent years. All of the major ‘skin mimic systems’ are considered
including: in vitro models using synthetic membranes, mathematical models including quantitative structurepermeability
relationships (QSPRs), human skin equivalents and chromatographic based methods. All of these
model based systems are ideally trying to achieve the same end-point, namely a reliable in vitro-in vivo correlation,
i.e. matching non-in vivo obtained data with that from human clinical trials. It is only by achieving this aim, that
any new method of obtaining permeation data can be acknowledged as a potential replacement for animal studies, for the determination
of transdermal permeation. In this review, the relevance and potential applicability of the various models systems will also be discussed.
Keywords: In vitro, measurement, permeation, skin, transdermal.
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