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A growing body of literature has marked the emergence and spread of antifungal resistance among species of Trichophyton, the most prevalent cause of toenail and fingernail onychomycosis in the United States and Europe. We review published data on rates of oral antifungal resistance among Trichophyton species; causes of antifungal resistance and methods to counteract it; and in vitro data on the role of topical antifungals in the treatment of onychomycosis. Antifungal resistance among species of Trichophyton against terbinafine and itraconazole-the two most common oral treatments for onychomycosis and other superficial fungal infections caused by dermatophytes-has been detected around the globe. Fungal adaptations, patient characteristics (e.g., immunocompromised status; drug-drug interactions), and empirical diagnostic and treatment patterns may contribute to reduced antifungal efficacy and the development of antifungal resistance. Antifungal stewardship efforts aim to ensure proper antifungal use to limit antifungal resistance and improve clinical outcomes. In the treatment of onychomycosis, critical aspects of antifungal stewardship include proper identification of the fungal infection prior to initiation of treatment and improvements in physician and patient education. Topical ciclopirox, efinaconazole and tavaborole, delivered either alone or in combination with oral antifungals, have demonstrated efficacy in vitro against susceptible and/or resistant isolates of Trichophyton species, with low potential for development of antifungal resistance. Additional real-world long-term data are needed to monitor global rates of antifungal resistance and assess the efficacy of oral and topical antifungals, alone or in combination, in counteracting antifungal resistance in the treatment of onychomycosis., (© 2024 The Authors. Mycoses published by Wiley-VCH GmbH.)

Background: Studies investigating the penetration of amorolfine through the nail have shown the highest concentration in the uppermost layer and measurable antifungal activity even in the lower layers of the nail., Objectives: This pilot, ex vivo study compared the penetration of antifungal concentrations of amorolfine 5% nail lacquer in different layers of healthy, human cadaver toenails with that of terbinafine 10% nail solution, ciclopirox 8% nail lacquer and naftifine 1% nail solution. Moreover, the effect of nail filing prior to application on the penetration of amorolfine 5% was assessed., Methods: Unfiled (n = 3) and filed (n = 3) nails were used for each antimycotic agent and amorolfine 5% nail lacquer, respectively. Twenty-four hours after topical application, the nails were sliced (10 μm), solubilised and added to agar plates seeded with Trichophyton rubrum. Zones of growth inhibition were measured., Results: Only amorolfine penetrated the nails at sufficient concentrations to inhibit growth of T rubrum at different nail depths. In contrast, the comparators did not show antifungal efficacy. Nail filing resulted in larger zones of inhibition for amorolfine compared with those of intact nails., Conclusions: Unlike its comparators, a single application of amorolfine 5% nail lacquer resulted in antifungal efficacy within the nail plate. Nail filing increased the antifungal efficacy of amorolfine 5% nail lacquer., (© 2019 Blackwell Verlag GmbH.)