Pharmacodynamics of fluconazole, itraconazole, and amphotericin B against Candida albicans

Abstract

The objective of this study was to evaluate the pharmacodynamic activity of fluconazole, itraconazole, and amphotericin B against Candida albicans. Susceptibilities were determined according to the NCCLS guidelines (M27). Time-kill studies were performed using antifungal concentrations of 0.25-32 x MIC. Samples were withdrawn at predetermined timepoints, then plated using a spiral plater. Colony counts were determined after incubation at 35 degrees C for 24 h. The AUKC(0-48) was plotted against the concentration/MIC ratio. Candida isolates (95-2672, 96-15, and 95-2542) were classified as susceptible, susceptible-dose dependent, and resistant to fluconazole and itraconazole (MIC = 0.25 and 0.03 microg/mL, 32 and 0.5 microg/mL, 64 and 1 microg/mL; respectively). All three isolates were susceptible to amphotericin B (MIC = 0.13 microg/mL). Fluconazole inhibited the growth of the susceptible and S-DD isolates and was ineffective at all concentrations against the resistant isolate. Itraconazole, on the other hand, inhibited growth of the susceptible isolate, but was ineffective for the S-DD and resistant isolates. Maximal effectiveness was noted at the concentration 8 x MIC and 2 x MIC for fluconazole and itraconazole, respectively. Amphotericin B demonstrated concentration-dependent antifungal activity. The times necessary for the colony counts to fall below the limit of quantification were inversely related to increasing concentrations of amphotericin B. The maximal effect for amphotericin B was recorded at 2 x MIC. In summary, the triazoles inhibit growth of susceptible C. albicans; however, careful consideration should be given to the MIC for S-DD isolates because itraconazole may not be active if the MIC is reported in the higher susceptible-dose dependency range. In reference to amphotericin B, optimal activity may be achieved by maximizing the peak drug concentration/MIC ratio.