Effect of hydration on the permeation of ketoconazole through human nail plate in vitro

The impact of hydration on the permeation of the antifungal drug, ketoconazole, through excised human nails in vitro was evaluated in diffusion cell studies. Nails treated with [3H]ketoconazole solvent-deposited onto the dorsal surface were maintained in incubators at 32 °C and exposed sequentially to relative humidities (dorsal side) of 15, 40, 80 and 100% over a period of 40 days. The ventral side was bathed in a pH 7.4 phosphate buffer. Ascending and descending humidity regimens were tested. Increasing the ambient RH from 15 to 100% enhanced permeation of radiolabel associated with [3H]ketoconazole by a factor of three. Diffusivities estimated from these data and the associated nail water contents (estimated in a separate study) can be described by a free volume theory. Therefore, formulations or treatments, which increase nail hydration, have potential to improve topical therapy for onychomycosis, if a favorable balance between drug delivery and growth conditions for the dermatophytes can be achieved.