In vitro activities of four antifungal drugs against Trichophyton rubrum isolates exhibiting resistance to fluconazole

Summary Thirty‐two clinical isolates of Trichophyton rubrum exhibiting resistance to fluconazole [minimum inhibitory concentrations (MICs) ≥ 64 μ g ml −1 ] were selected to test the antifungal activity of ketoconazole, itraconazole, griseofulvin and terbinafine. We followed the guidelines of the National Committee for Clinical Laboratory Standards for testing filamentous fungi. The strains Candida parapsilosis (ATCC 22019), Candida krusei (ATCC 6258), T. rubrum (ATCC 40051) and Trichophyton mentagrophytes (ATCC 40004) were included for quality control. The microdilution plates were incubated at 28 °C and were read visually after 7 days of incubation and endpoint determination readings were performed visually. The MIC ranges for the four antifungals were: 0.0625–2 μ g ml −1 for ketoconazole, 0.25–2.0 μ g ml −1 for griseofulvin, ≤0.031–1.0 μ g ml −1 for itraconazole and ≤0.031 μ g ml −1 for terbinafine (for all tested isolates). Terbinafine was the most potent drug against T. rubrum , in vitro , followed by itraconazole, ketoconazole and griseofulvin. Much work is still needed to correlate the MICs of these drugs with clinical outcomes to develop interpretative breakpoints for T. rubrum and other dermatophytes.