Synergistic action of amphotericin B and rifampin against Candida species.

Amphotericin B and rifampin act synergistically against certain yeasts in vitro. Whether this synergism is a general phenomenon or whether the effect has strict species and strain requirements was studied. Included in a survey of the genus Candida were eight human isolates of Candida albicans and one strain each of Candida krusei, Candida tropicalis, Candida pseudotropicalis, Candida parapsilosis, Candida guilliermodnii, and Candida stellatoidea. Cultures in both control and drug-containing liquid medium were incubated at 37 C with aeration. Effects of the drugs were determined from viability assays performed at zero-time and at 17 hr. Amphotericin C and rifampin were judged to be synergistic if any one of three different sets of criteria was met. Combined activity greater than the sums of individual drug effects was required in each set of criteria. Partially inhibitory or fungistatic levels of amphotericin B and noninhibitory concentrations of rifampin acted synergistically against all strains of Candida examined. Within the genus Candida, synergism of amphotericin B and rifampin appears to be a rather general phenomenon.