Comparison of posaconazole and voriconazole in vitro killing against Candida krusei

The in vitro activity of posaconazole and voriconazole was evaluated by MIC, minimum fungicidal concentration (MFC), and time-kill methods. MFCs were determined for 15 Candida krusei and time-killing curves for 5 of these isolates. MFCs were obtained transferring 100 μL from clear MIC wells onto Sabouraud dextrose agar. Time-kill studies were performed in RPMI 1640 medium (5 mL, inoculum ≈105 colony-forming unit [CFU]/mL). Geometric mean (GM) MIC and GM-MFC were 0.2 and 0.72 mg/L for posaconazole and 0.4 and 2.64 mg/L for voriconazole. The killing rate was isolate and concentration dependent; reductions in CFUs start at ≥0.12 mg/L (posaconazole) and ≥0.5 mg/L (voriconazole). The mean time to reach a 90% growth reduction was 41.5 ± 14.2 h (8 mg/L posaconazole) and 48.7 ± 61.3 h (32 mg/L voriconazole). By time kill, a 99% killing rate was not reached by either agent. Both methods demonstrated that posaconazole (more active and greater killing rate) and voriconazole have fungicidal activity against C. krusei.