Physicochemical Aspects of Percutaneous Penetration and Its Enhancement |
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Authors: | Guy Richard H. Hadgraft Jonathan |
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Affiliation: | (1) Departments of Pharmacy and Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, 94143;(2) The Welsh School of Pharmacy, University of Wales, Cardiff, Cardiff, CF1 3XF, Wales |
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Abstract: | The classic diffusion model-based interpretation of percutaneous absorption is compared to a simple kinetic analysis. The physicochemical significance and the major deductions of the two approaches are shown to be in general agreement. In particular, the effect of penetrant oil/water partition coefficient on transdermal flux is consistently predicted by the two models. Diffusional and kinetic assessments of skin penetration enhancement are then shown to reveal similar dependencies upon penetrant physical chemistry. It is demonstrated that the requirements for successful promotion of a lipophilic drug's transdermal flux are quite different from those necessary for a hydrophilic penetrant. Finally, in light of published transport data and our increased comprehension of the stratum corneum barrier function, the evidence for (and significance of) different absorption paths across the stratum corneum is considered. In addition, the impact of penetrant size on transport is addressed. It is argued that currently held beliefs concerning (i) a putative polar route through the stratum corneum and (ii) the dependence of flux on molecular weight warrant considerable further attention before their unequivocal acceptance is appropriate. |
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Keywords: | percutaneous absorption skin penetration transport kinetics permeation, skin enhancement, skin absorption |
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