Combined in vitro activity of amphotericin B and 5-fluorocytosine against Cryptococcus neoformans and Candida albicans.

The in vitro combined antifungal activity of amphotericin B (AMB) and 5-fluorocytosine (5-FC) against 10 strains of Candida albicans and 8 strains of Cryptococcus neoformans was studied. Serial twofold dilutions of AMB (0.1 to 12.8 micrograms/ml) were tested with serial twofold dilutions of 5-FC (0.39 to 400 micrograms/ml) by using the broth dilution method. A synergistic effect was seen for 17 strains with 50 micrograms of 5-FC per ml added to AMB. Only one strain was killed by 0.8 micrograms per ml or less of AMB alone, whereas all strains were killed with the addition of 50 micrograms of 5-FC per ml.