An in vitro and in vivo study on the synergistic effect and mechanism of itraconazole or voriconazole alone and in combination with tetrandrine against Aspergillus fumigatus

In this study, we investigated the in vitro antifungal effects of itraconazole/voriconazole (ITR/VRC) alone and in combination with tetrandrine (TET) against 23 clinical isolates of A. fumigatus using a chequerboard microdilution method. The dynamic antifungal effects of TET with ITR/VRC against A. fumigatus were assessed in vivo using time-kill curves following systemic infection of mice with A. fumigatus. After treatment, efflux pump activity was determined by the efflux of rhodamine 6G (R6G). When ITR was combined with TET, ITR MICs were reduced from 0.125-32 to 0.0625-2 μg ml(-1), and TET MICs were reduced from 256-512 to 8-64 μg ml(-1). When VRC was combined with TET, VRC MICs were reduced from 0.125-2 to 0.03125-0.5 μg ml(-1), and TET MICs were reduced from 256-512 to 8-256 μg ml(-1). Time-kill curves revealed that A. fumigatus viability was reduced after treatment with ITR/VRC combined with TET versus ITR/VRC alone. ITR/VRC combined with TET significantly prolonged mouse survival and reduced kidney and brain tissue burdens versus ITR/VRC alone (P < 0.05). Moreover, TET inhibited R6G efflux of A. fumigatus. Thus, in vitro and in vivo, TET acted synergistically with ITR/VRC against A. fumigatus, and the synergistic mechanism was related to inhibition of the drug efflux pump.