Quantitative determination of fluconazole-amphotericin B antagonism to Candida albicans by agar diffusion.

Fluconazole is a bis-triazole antifungal which partly antagonizes the activity of amphotericin B against Candida albicans (and other Candida species). This antagonism can easily be demonstrated by radial agar diffusion. Amphotericin B at reservoir concentrations of up to 1.2 mg l-1 showed a diffusion behaviour which was described by means of a simple mathematical analysis. Therefore quantitative determination of the antagonism was possible. Using a reference strain of Candida albicans, the critical concentration of amphotericin B was increased by fluconazole up to 2.4-fold.