Influence of human serum on the postantifungal effect of four antifungal agents on Candida albicans.

This study evaluates the influence of both fresh and heated human serum on the postantifungal effect (PAFE) induced by different concentrations of amphotericin B (AmB), 5-fluorocytosine (5-Fc), Ketoconazole (Kz) and fluconazole (Flu) on two strains of Candida albicans. The concentrations were selected in harmony with the pharmacokinetic properties and toxicity of the drugs. Without serum there was no delay in the growth of yeast cultures pretreated with Kz or Flu, leading to negative PAFEs, however with AmB and 5-Fc the PAFEs were positive. When assays were made in the presence of 10% fresh human serum, the duration of the PAFEs increased with all drugs tested, and those induced by azolic agents became positive. In the presence of 10% human serum heated at 56 degrees C for 30 min, the PAFEs of the antifungal agents were similar to those obtained in the absence of serum. Our results suggest that fresh serum positively influenced PAFE which may be an important factor in determining the dosing regimen for infection by yeasts.