Abstract:
Our objective was to screen mols. that could interact with keratin in the human nail and thereby improve the topical penetration of actives into and through the nail plate. We used specialized Franz-type diffusion cells for our permeation expts. and water as a marker mol. Aq./hydroalcoholic gels contg. the enhancers were spiked with tritiated water and compared with a control (without enhancer). We computed the normalized water flux (defined as a product of flux and nail thickness) for each gel. We defined an enhancement factor for water as the ratio of the normalized water flux from a gel contg. enhancer to that of the control. Our results indicate that the chem. structure of the modifier is most important in detg. its ability to enhance penetration. The best enhancement effect was obtained using N-(2-mercaptopropionyl) glycine, a mercaptan deriv. of an amino acid, in combination with urea. The concn. of each chem. modifier was linearly related to normalized water flux and mercaptan levels were more important that urea levels in penetration enhancement. Barrier integrity of nails was compromised after treatment with effective chem. modifiers. Thus, we have developed a suitable technique to screen nail penetration enhancers using water as a probe.