The antifungal activities of the
essential oil from Agastache rugosa and its main component,
estragole, combined with
ketoconazole, one of the
azole antibiotics commonly used to treat
infections caused by Trichophyton species, were evaluated in this study. The combined effects were measured by the checkerboard microtiter and the disk diffusion tests, against T. erinacei, T. mentagrophytes, T. rubrum, T. schoenleinii and T. soudanense. Susceptibility of the five Trichophyton species to the oil alone, or
ketoconazole alone, differed distinctly. The fractional inhibitory concentration indices (FICI) of
ketoconazole combined with
estragole or A. rugosa
essential oil, against the tested Trichophyton species, were between 0.05 and 0.27, indicating synergistic effects. These
drug combinations exhibited the most significant synergism against T. mentagrophytes, with FICIs of 0.05 and 0.09 for
estragole and the
essential oil fraction from A. rugosa, respectively. Isobolograms based on the data from checkerboard titer tests also indicated significant synergism between
ketoconazole and the Agastache oil fraction or
estragole, against the Trichophyton species evaluated. Trichophyton susceptibility to
ketoconazole was significantly improved by combination with the Agastache rugosa oil fraction or its main component,
estragole.