Abstract:The aim was to detect the in vitro antifungal interactions between tetrandrine (TET) and itraconazole (ITC) against Aspergillus fumigatus. According to the Clinical and Laboratory Standards Institute(CLSI) M38-A2 guidelines, we used 21 clinical isolates of Aspergillus fumigatus to evaluate the response through the checkerboard microdilution method. We employed the spectrophotometric method to determine the results of the interactions, and the nature of interactions was assessed by the fractional inhibitory concentration index (FICI) model. The result was also verified by isobologram with AF46 as sample. The MICs of TET and ITC alone were 256~512 μg/mL、0.125~32 μg/mL, respectively. While the MICs of TET and ITC in combination were 8~64 μg/mL and 0.03~2 μg/mL, with the disappearance of the so-called “trailing” phenomenon. The FICI of the drugs in combination ranged from 0.08~0.38, revealing strong synergism between TET and ITC. Synergism was also demonstrated in that the corresponding isobole of AF46 was concave. Our findings suggest that when combined with ITC, TET showed potent synergism in antifungal activity.