In Vitro Resistance and Evolution of Resistance to Tavaborole in Trichophyton rubrum

Abstract

Tavaborole is currently used in the topical treatment of onychomycosis. In this study, we analyzed the in vitro emergence/evolution of resistance against tavaborole in Trichophyton rubrum. When T. rubrum strains were propagated on media containing the MIC of tavaborole, spontaneous resistant mutants were isolated at a frequency of 10⁻⁸. The frequency was almost 100-fold higher following fungal growth in the presence of a sub-inhibitory tavaborole concentration (0.5-fold the MIC) for ten transfers. All collected mutants showed similar 4- to 8-fold increase in the drug minimal inhibitory concentration. No cross-resistance to other antifungals was evidenced.