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 ofTrichophyton mentagrophytes andTrichophyton rubrum in a yeast carbon broth medium incorporating Alamar Blue dye. The proposed MIC with keratin impregnation (MICK ) 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 forT. mentagrophytes and ≤0.063 μg/ml forT. rubrum , were approximately half of those of clotrimazole for the same isolates. The superiority of the MICK s of amorolfine for isolates ofT. mentagrophytes (2.0 μg/ml; range, 0.5 to 8.0 μg/ml) andT. 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.