Solvent effects in permeation assessed in vivo by skin surface biopsy

Research performed at:

1. Laboratório de Fisiologia Experimental & UCTF – Faculdade de Farmácia da Universidade de Lisboa, Av das Forças Armadas, Lisboa, Portugal.

2. Unidade de Dermatologia Experimental, Universidade Lusófona, Campo Grande 376, Lisboa, Portugal.

The authors:

Catarina Rosado, Luis Monteiro Rodrigues.

Transdermal drug delivery has become an important means of drug administration. It presents numerous advantages but it is still limited by the small number of drugs with a suitable profile. The use of solvents that affect the skin barrier function is one of the classic strategies of penetration enhancement. Some of these solvents have well characterised actions on the stratum corneum, but the majority are still selected using empirical criteria.

The objective of this work was to conduct a systematic study on the ability to affect skin permeation of solvents commonly used in transdermal formulations. An innovative methodology in this area was employed, consisting of the combination of skin surface biopsy with colorimetry.

The study compared in vivo differences in the permeation of a hydrophilic (methylene blue) and a lipophilic (Sudan III) dye, after treatment of the skin with different vehicles. Consecutive skin surface biopsies of each site were taken and the cumulative amounts of the dyes in the stripped stratum corneum were measured by reflectance colourimetry.

This study has only superficially explored the potential of the combination of skin surface biopsy and colourimetry, but the encouraging results obtained confirm that the methodology can be extended to the study of more complex formulations.