Comparative studies on the postantifungal effect produced by the synergistic interaction of flucytosine and amphotericin B on Candida albicans.

A turbidometric method was used to measure Candida albicans yeast cell growth and to quantitate the postantifungal effect (PAFE) after exposure to various concentrations of flucytosine and amphotericin B, alone and in combination, for 2 hr at 30 degrees C. The drug concentrations used in the PAFE assays were determined by initial MIC and FIC (fractional inhibitory concentration) evaluations. The PAFE was calculated by the difference in time (hr) required for growth of the control and test cultures to reach the 0.5 absorbance level following removal of the drug by dilution. A synergistic PAFE was evidenced with combinations of the two drugs at concentrations below their individual MICs. Combinations of flucytosine (0.012 to 0.049 micrograms ml-1) and amphotericin B (0.195 to 0.39 micrograms ml-1) produced PAFEs ranging from 6.3 to 21.8 hr. These PAFEs persisted from 0.3 to 14.7 hr longer than those achieved when each of the two agents was assayed separately.