Susceptibility of Trichophyton rubrum to griseofulvin

Two hundred and seventy isolates of Trichophyton rubrum from 182 patients were subjected to susceptibility testing with griseofulvin according to Granade & Artis. A slight modification of the method concerning homogenization procedures gave better growth of controls in our investigation. In 245 cases an MIC could be determined. Among these isolates, seven strains from six patients presented MICs between 2 and 3 micrograms griseofulvin per ml, a value which, according to Artis et al., is to be considered as relatively resistant. The other isolates proved to be more susceptible to griseofulvin. Three of the patients showed no indication of therapeutic failure of griseofulvin treatment. The other three patients had onychomycoses of long standing and had been treated with griseofulvin previously with little or limited success. It is our conclusion that griseofulvin susceptibility testing is not a reliable instrument in explaining failure of griseofulvin therapy in Trichophyton rubrum mycoses.