Differential activity of triazoles in two-drug combinations with the echinocandin caspofungin against Aspergillus fumigatus.

OBJECTIVES We investigated the in vitro activity of various triazoles in two-drug combinations with the echinocandin caspofungin against clinical isolates of Aspergillus fumigatus. METHOD Conidial suspensions were prepared from 20 clinical isolates of A. fumigatus highly susceptible to itraconazole, voriconazole, posaconazole and ravuconazole (MIC-0 range 0.125-1 mg/L), and caspofungin (MIC-0 range 32-64 mg/L). The in vitro susceptibility of A. fumigatus to two-drug combinations of itraconazole, voriconazole, posaconazole and ravuconazole with caspofungin was evaluated by the fractional inhibitory concentration index (FICI) method. RESULTS Two-drug combinations of caspofungin with itraconazole (FICI = 0.49 +/- 0.04) or posaconazole (FICI = 0.32 +/- 0.09) provided synergic interaction. On the other hand, ravuconazole (FICI = 0.61 +/- 0.31) and voriconazole (FICI = 1.61 +/- 0.42) in combination with caspofungin showed no interaction against A. fumigatus. CONCLUSIONS Our data show that the in vitro antifungal efficacies of combinations of members from two different classes are not always similar and hence are not predictable.