In Vitro Skin Penetration Studies

As described previously in this chapter, efforts have been made to develop methods for quantification of skin permeability, validation of diffusion cell setups, and correlation of in vitro data with the in vivo situation. However, the average drug permeation experiment does not provide insight into the temporal and local disposition within the tissue, that is, the skin penetration. The following discussion will give an overview of methods tackling this kind of problem. 

Drug levels within the stratum corneum can be assessed by sampling single corneocyte layers with adhesive film. The drug is then extracted from the tape-strips and quantified by a suitable analytical method. Usually, scintillation counting (for radioactive compounds) or high performance liquid 

The tape-stripping technique has been applied in vivo, as well as in vitro. The used in vitro incubation devices are the same as described for skin permeation studies. A specialized incubation device developed by Loth and coworkers, the Saarbriicken penetration model, allows investigation of skin penetration bypassing the normally occurring nonphysiological hydration of the dermis [64], 

To show the substance distribution in the different skin layers, the allocation of the different removed skin segments, obtained either by a stripping procedure or by cryo-cutting, is essential. 

In the following section, methods of assessing the thickness of stratum corneum removed per tape are summarized. 

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