Background Matrix-assisted laser desorption ionisation mass spectrometry imaging (MALDI-MSI) is a mass spectrometry-based technique, which can be applied for compound-specific imaging of pharmaceuticals in tissues samples. MALDI-MSI technology is widely used to visualise penetration and distribution profile through different tissues but has never been used with nail tissue.

Objectives This study used MALDI-MSI technology to visualise distribution profile and penetration into ex vivo human mycosis-infected toenails of three antifungal active ingredients amorolfine, ciclopirox and naftifine contained in topical onychomycosis nail treatment preparations, marketed as Loceryl(R), Ciclopoli(R) and Exoderil(R).

Methods Three mycosis-infected toenails were used for each treatment condition. Six and twenty-four hours after one single topical application of antifungal drugs, excess of formulation was removed, nails were cryo-sectioned at a thickness of 20 mu m, and MALDI matrix was deposited on each nail slice. Penetration and distribution profile of amorolfine, ciclopirox and naftifine in the nails were analysed by MALDI-MSI.

Results All antifungal actives have been visualised in the nail by MALDI-MSI. Ciclopirox and naftifine molecules showed a highly localised distribution in the uppermost layer of the nail plate. In comparison, amorolfine diffuses through the nail plate to the deep layers already 6 hours after application and keeps diffusing towards the lowest nail layers within 24 hours.

Conclusions This study shows for the first-time distribution and penetration of certain antifungal actives into human nails using MALDI-MSI analysis. The results showed a more homogeneous distribution of amorolfine to nail and a better penetration through the infected nails than ciclopirox and naftifine.