Synergistic anti-candidal activity of tetrandrine on ketoconazole: an experimental study

With the widespread use of azoles, drug resistant Candida albicans strains are increasing. The study examined the synergism of tetrandrine (TET) on ketoconazole (KCZ) candidacidal activity. The protocol M27-A2 of the Clinical and Laboratory Standards Institute (CLSI) was adopted and the minimum inhibitory concentrations (MICs) were determined for KCZ alone and in combination with a TET level that was noncytotoxic for C. albicans strains CA-1 through CA-17, with no CA-10. Colony counting techniques were used to construct time-kill curves. CA-15 was used to build the mouse candidal vaginitis model. After randomization, drugs were administered vaginally once daily from days 3-10 (both KCZ and TET were 26 mg/kg/day and 13 mg/kg/day, respectively, administered in different combinations). Mouse vaginal lavage fluid was obtained at days 2, 6, and 11 after inoculation for fungal load analysis, and vaginal tissue was obtained for pathological examination. MICs of KCZ alone and combined with 30 microg/mL TET for the C. albicans strains were 1-32 microg/mL and 0.0038-0.2500 microg/mL, respectively ( T = 24.624, p = 0.000). Time-kill curves showed that at 48 h the viable cell counts of strains treated with KCZ + TET were at least 2 log(10) CFU/mL lower compared to strains treated with corresponding doses of KCZ (p = 0.000). At day 6, the fungal load in the KCZ 26 mg/kg/day + TET 26 mg/kg/day mice was significantly lower than the KCZ 26 mg/kg/day mice (1.17 +/- 1.17 x 10(4) CFU/mL and 9.33 +/- 3.08 x 10(4) CFU/mL, respectively, p = 0.000). Mucosal and submucosal fungal clearances were complete and vaginal mucosal edema was slight with minimal inflammatory cell infiltration. We conclude that noncytotoxic doses of TET synergistically enhance KCZ candidacidal activity in vitro and in vivo.