Hydration of nail plate: A novel screening model for transungual drug permeation enhancers

Drug delivery by topical route for the treatment of onychomycosis, a nail fungal infection, is challenging due to the unique barrier properties of the nail plate which imparts high resistance to the passage of antifungal drugs. Permeation enhancers are used in transungual formulations to improve the drug flux across the nail plate. Selection of the effective permeation enhancer among the available large pool of permeation enhancers is a difficult task. Screening the large number of permeation enhancers using conventional Franz diffusion cells is laborious and expensive. The objective of present study was to evolve a simple, accurate and rapid method for screening of transungual drug permeation enhancers based on the principle of hydration of nail plate. The permeation enhancer which affects the structural or physicochemical properties of nail plate would also affect their hydration capacity. Two screening procedures namely primary and secondary screenings were evolved wherein hydration and uptake of ciclopirox olamine by nail plates were measured.Hydration enhancement factor, HEF24 and drug uptake enhancement factor, UEF24 were determined for screening of 23 typical permeation enhancers. The Pearson's correlation coefficient between HEF24 and UEF24 was determined. A good agreement between the HEF24 and UEF24 data proved the validity of the proposed nail plate hydration model as a screening technique for permeation enhancers.