Penetration Profiles of Four Topical Antifungals in Mycotic Human Toenails Quantified by Matrix-Assisted Laser Desorption Ionization-Fourier Transform Ion Cyclotron Resonance Imaging.

Introduction: Onychomycosis is a fungal infection of the nails that can be challenging to treat. Here, matrix-assisted laser desorption ionization-Fourier transform ion cyclotron resonance (MALDI-FTICR) imaging was applied to the quantitative analysis of the penetration profile of the antifungal compound, amorolfine, in human mycotic toenails. The amorolfine profile was compared with those of three other antifungals, ciclopirox, naftifine, and tioconazole.

Methods: Antifungal compounds (amorolfine 5% lacquer, ciclopirox 8% lacquer, naftifine 1% solution, and tioconazole 28% solution) were applied to mycotic nails (n = 42). Nail sections were prepared, and MALDI-FTICR analysis was performed on the sections at a spatial resolution of 70 μm to compare the distribution profiles. Based on the minimum inhibitory concentrations of the four test compounds needed to kill 90% (MIC) of the fungal organism, Trichophyton rubrum, the fold differences between the MIC and the antifungal concentrations in the nails (termed the multiplicity of the MIC) were calculated for each.

Results: The penetration profiles indicated higher concentrations of amorolfine and ciclopirox in the deeper layers of the nails 3 h after treatment, compared with naftifine and tioconazole. The mean concentrations across the entire nail sections at 3 h were significantly different among the four antifungals: amorolfine, 2.46 mM; ciclopirox, 0.95 mM; naftifine, 0.63 mM; and tioconazole, 1.36 mM (p = 0.016; n = 8 per compound). The median multiplicity of the MIC at 3 h was 191-fold for amorolfine, tenfold for ciclopirox, 52-fold for naftifine, and 208-fold for tioconazole.

Conclusion: In this study, MALDI-FTICR was successfully applied to the quantitative analysis of antifungal distribution in human mycotic nails. The findings suggest that amorolfine penetrates deeper layers of the nail and accumulates at concentrations far exceeding the MIC needed to exert antimycotic activity.