Amorolfine nail lacquer: a novel formulation

Abstract

Onychomycosis is difficult to treat. Systemic therapy with the potent oral azoles may be restricted by their potential side-effects; an attractive alternative is topical application of an antifungal directly to the nail. Several such formulations have been developed, including creams and lotions which are largely ineffective due to poor drug penetration into and through the nail structure. Nail keratin is thick and compact; its permeability is low. Transungual drug diffusion depends on the characteristics of the nail (especially degree of hydration) and the properties of the chemical (molecular weight and size, and lipophilic/hydrophilic profile). A nail lacquer containing 5% amorolfine was recently introduced; the volatile vehicle evaporates, leaving an occlusive film on the surface of the nail. The film acts as a drug depot, while at the same time increasing the hydration of the nail and the thermodynamic activity of the drug, thereby enhancing diffusion, particularly of hydrophilic compounds. Amorolfine has been shown to penetrate human nail from the film at clinically effective concentrations. In addition, the effect is long lasting: a single application of lacquer provides protection for 1 week. Release and rate of diffusion can be optimized by selecting the components of the lacquer formulation (solvent, polymer, plasticizer). Transungual drug delivery via nail lacquer is a major addition in the dermatologist's therapeutic arsenal.