In vitro activity of itraconazole in combination with terbinafine against clinical strains of itraconazole - insensitive Sporothrix schenckii

Four strains of Sporothrix schenckii were isolated from patients with cutaneous sporotrichosis who failed itraconazole (ITC) treatment. To investigate the susceptibility of these strains to ITC and terbinafine (TRB) alone and in combination in 2 growth phases in vitro, a checkerboard microdilution method was used in accordance with the recommendations of the Clinical Laboratory Standards Institute (CLSI) was used in our study. The drug interaction was evaluated by assessing the fractional inhibitory concentration index (FICI). The geometric means (GMs) of the minimum inhibitory concentrations (MICs) of 4 insensitive strains were obviously higher than those of the sensitive isolates used for comparison. The FICI analysis revealed that only 2 isolates (25%) were synergistic in yeast form. Our results indicate the failure of clinical treatments might be caused by the insensitivity to ITC of these strains.