In vitro activities of amphotericin B in combination with four antifungal agents and rifampin against Aspergillus spp.

Strains of Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger were tested for in vitro susceptibility with a microtiter plate system in buffered yeast-nitrogen base and in buffered minimal essential medium. Isolates were tested against amphotericin B, flucytosine, rifampin, ketoconazole, ICI 153,066, and Bay n 7133 and against combinations of amphotericin B with each of the other five drugs. Combinations of amphotericin B and rifampin were the most active against all three species of Aspergillus. Flucytosine combined with amphotericin B produced little or no reduction of the MICs at which 90% of the strains were inhibited compared with amphotericin B alone. With one exception, the addition of ketoconazole, ICI 153,066, or Bay n 7133 to amphotericin B did not consistently alter the MICs. The addition of ICI 153,066 markedly increased the MICs of amphotericin B against the A. flavus isolates in both media. When the azoles were tested alone, Bay n 7133 was the most active against A. fumigatus, but was two- to fivefold less active against A. flavus. Ketoconazole was the most active azole against A. flavus.