Abstract:
A review with 51 refs. The human nail forms a resistant barrier to the topical penetration of actives. Thus, treatment of nail disorders, such as fungal infections, remains a challenge because of the difficulty encountered in achieving therapeutic concns. of drugs at the site of infection. The nail is primarily composed of a highly cross-linked keratin network that contains several disulfide linkages. This unique structure results in a highly effective permeability barrier. Nail penetration has been reported to be affected by mol. size and hydrophilicity; smaller, water-sol. mols. are found to preferentially permeate the nail. Permeation of undissociated drugs is favored in certain instances. Also, some studies indicate that the nature of the vehicle can influence drug penetration. Recent research has focused on improvement of penetration of topically applied actives into and through the nail. Studies have shown that compds. contg. sulfhydryl groups in conjunction with keratolytic agents can significantly enhance drug penetration, relative to a control formulation (without enhancer). Such sulfhydryl compds. are thought to reduce the disulfide linkages in the nail keratin matrix. Thus, although some success has been achieved in enhancing penetration of drugs through the nail, further research is required to achieve successful topical products for treatment of nail infections.