Fluorometric Assessment of In Vitro Antidermatophytic Activities of Antimycotics Based on Their Keratin-Penetrating Power

Keratin particles impregnated with amorolfine or clotrimazole in serial doubling dilutions (64 to 0.125 μg/ml) were used to evaluate the activities of these agents against 20 isolates each of Trichophyton mentagrophytes and Trichophyton rubrum in a yeast carbon broth medium incorporating Alamar Blue dye. The proposed MIC with keratin impregnation (MIC(K)) is defined as the lowest concentration of an agent used to impregnate keratin particles that effects a fluorescence-based fungal growth quotient of 0.05 or less. The conventional colorimetric and visual MICs of amorolfine for the dermatophytes, ≤0.03 μg/ml for T. mentagrophytes and ≤0.063 μg/ml for T. rubrum, were approximately half of those of clotrimazole for the same isolates. The superiority of the MIC(K)s of amorolfine for isolates of T. mentagrophytes (2.0 μg/ml; range, 0.5 to 8.0 μg/ml) and T. rubrum (4.0 μg/ml; range, 2.0 to 8.0 μg/ml) over those of clotrimazole (32 μg/ml [range, 8.0 to >64 μg/ml] and 64 μg/ml [range, 16 to >64 μg], respectively) may indicate the strong in vivo antidermatophytic activity of amorolfine as a topical agent. The new antidermatophytic susceptibility testing procedure has potential clinical utility for the in vitro screening of agents for use in the topical treatment of superficial mycoses.