The Presence of an Air Gap Between the Nail Plate and Nail Bed in Onychomycosis Patients: Treatment Implications for Topical Therapy

Background: Transungual nail penetrance has traditionally been considered to be the only route of delivery for topical antifungals in onychomycosis. Subungual penetrance may be an alternate route of delivery. Objective:To evaluate the ability of efinaconazole vehicle solution to reach the site of toenail onychomycosis through application to the hyponychium or hyponychium and dorsal nail surface, and assess the impact of the air gap between the nail plate and nail bed. Methods:Twenty-three participants with moderate to severe, mycologically-confirmed onychomycosis were enrolled (mean age, 48.5 years). Two separate applications of vehicle solution containing fluorescein for visualization were applied at the hyponychium or hyponychium and dorsal nail surface. Affected nails were later clipped to allow examination of the nail bed and further examination of the ventral surface of the nail. Spread of formulation was assessed under visible and UV light conditions by photographing target toenails after vehicle application and after nail clipping. Results: There was a positive correlation between the size of the air gap and degree of affected nail involvement (R-2=0.064). Assessments under both visible and UV light indicated that the vehicle had spread to the site of infection, with deposition of fluorescein wherever vehicle had reached, irrespective of application methodology or size of air gap. Nail clippings also indicated absorption into the ventral surface of the nail plate. Limitations:The relative contributions of subungual versus transungual application of drug to the nail plate to the efficacy of efinaconazole topical solution, 10% in treating onychomycosis were not assessed. Conclusions:This study suggests that the low surface tension vehicle developed for efinaconazole topical solution, 10% can reach the site of infection by application to the hyponychium, dorsal or ventral nail surface and nail folds. This multidirectional approach to drug delivery at the site of fungal infection may contribute to the magnitude of efficacy seen in clinical trials.