Physical signatures of drug transport through an artificial skin barrier--a proposed model and its validation.

The objective of the present study is to better characterize the system acting as a model for the penetration of a pharmaceutical drug into the skin. With a new mathematical formalism, the transport of the drug (dithranol) from a semisolid vaseline suspension into an artificial membrane was described. In our novel approach, we have taken into account not only diffusion but also other effects dependent on chemical reactivity of drug, medium structure, and drug-matrix interactions. The transport equation was solved with two methods: the Laplace transform and the reflection-and-superposition. Despite the applied method, the three-dimensional calculations were found to be, in major parts, in good agreement with the experimental data resulting from the photoacoustic depth profiling. For the first time, from the depth profiling we were capable of estimating not only the diffusion coefficient but also other parameters of the permeation phenomenon as the pore velocity, the first and the zero order reaction rate coefficients.