Background: Echinocandins are an important new class of antifungal agents. The therapeutic potential for the combination of antifungal triazoles and echinocandins in enhancing antifungal activity is not well understood and is the focus of this study. Methods: Three methodologies were utilized to evaluate the in vitro interaction of caspofungin (CFG) and micafungin (MFG) in combination with voriconazole (VCZ) against 3 isolates of A. fumigatus: checkerboard microdilution assay, time-sequenced MTT hyphal damage assay and a fluorescent membrane probe, dihexyloxacarbocyanine iodide (DiOC6) assay for cell viability. RPMI medium was used in all assays. Results: Checkerboard microdilution: The median fractional inhibitory concentration index (FICI) for VCZ plus MFG was 0.87 (range 0.48 - 2.0) at 24h incubation and 0.51 (0.26 - 2.0) at 48h. The median FICI for VCZ plus CFG was 0.75 (0.49 - 2.0) at 24h and 0.51(0.5- 1.2) at 48h. These data demonstrate an additive effect for the both drug combinations at two time points. The median fluorescence FICI for VCZ combined with MFG was 0.62 (0.24 - 1.2), at 48h, demonstrating an additive effect. MTT assay: VCZ plus MFG and VCZ plus CFG combinations showed synergistic hyphal damage. VCZ (0.25mg/ml) and MFG (0.25mg/ml-32mg/ml) combinations, in 18/18 experiments, at 12h and 24 h, displayed synergistic hyphal damage, with a mean of 52.7% Â± 2.2 and 58.9% Â± 3.16 respectively. VCZ (0.25mg/ml) and CFG (0.06-8mg/ml) combinations, in 15/15 experiments, at 12h and 24h, displayed synergistic hyphal damage with a mean of 56.3 % Â± 6.4.and 35.3% Â± 2.7 respectively. Conclusion: The in vitro interaction between two echinocandins and voriconazole was found to have an additive effect against A. fumigatus using a checkerboard microdilution method and a fluorescent membrane probe. The MTT assays demonstrated a time dependent synergistic hyphal damage at 12h and 24h incubation.
Full conference title:
42nd Interscience Conference on Antimicrobial Agents and Chemotherapy
- ICAAC 42nd