Antifungal effects of fluconazole (UK 49858), a new triazole antifungal, in vitro

Abstract

Fluconazole is a novel triazole antifungal intended for oral treatment of superficial and systemic mycoses. In tests done in standard mycological media, the compound had minimal inhibitory concentrations against pathogenic Candida species that were usually in excess of 100 mg/l. By contrast, its 'relative inhibition factors' against Candida species (calculated from areas under the antifungal dose-response curves) were of the same order as those of other imidazole and triazole antifungal agents. Against pathogenic Aspergillus species and dermatophytes, the mean relative inhibition factors were the highest so far recorded for an azole antifungal, indicating a relatively weak inhibitory activity against these fungi. Fluconazole inhibited branching and hyphal development in C. albicans at concentrations as low as 10(-6) M (0.3 mg/l), but miconazole and ketoconazole were still active in these tests at concentrations 100 times lower than this. The new antifungal did not suppress ATP concentrations in C. albicans spheroplasts, in common with other weakly lipophilic azole antifungals. This overall poor activity of fluconazole in vitro corresponds badly with its high activity in animal models of mycoses in vivo, and provides more evidence for the unreliability of tests with azole antifungals in vitro as predictors of potential efficacy in vivo.