Synergistic effect of ofloxacin and fluconazole against azole-resistant Candida albicans

We investigated the combination effects of ofloxacin and fluconazole against azole-resistant Candida albicans strains in vitro and in vivo. Ofloxacin alone showed no efficacy against the azole-resistant C. albicans strain, C26. The in-vitro combination effects were evaluated by the checkerboard method, calculated as the fractional inhibitory concentration (FIC) index, but there was no synergistic effect of the combination. The activity of the drug efflux pump in the azole-resistant C. albicans strains was measured by intracellular rhodamine 6G concentration. When the cells were incubated with ofloxacin or grepafloxacin, the intracellular rhodamine 6G concentration was significantly increased in the azole-resistant C. albicans strain. In-vivo combination effects were evaluated in murine disseminated candidiasis. The survival of the mice was not prolonged, but counts of the yeast cells in the kidney and spleen were reduced following treatment with the combination of ofloxacin (20 mg/kg) and fluconazole (20 mg/kg). The combination of ofloxacin and fluconazole may represent an effective strategy to treat infections caused by azole-resistant C. albicans. Received: March 10, 2000 / Accepted: May 17, 2000