Inhibitory effect of antifungal agents on germ tube formation in Candida albicans.

Summary: The allylamine derivatives naftifine and terbinafine were compared in vitro with 15 standard antifungals in terms of their inhibitory effects on the yeast‐mycelial (Y‐M) transformation in tests with 19 Candida albicans isolates. Y‐M transformation minimal inhibitory concentration (MICs) were determined in a microtiter‐broth‐dilution test using a chemically defined medium with N‐acetyglucosamine as inducer of hyphal growth. Clotrimazole was the most potent inhibitor with a geometric mean MIC (G‐MIC) value of 0.00038 μg ml‐1 followed by ketoconazole (G‐MIC,0.012 μg ml‐1) and itraconazole (G‐MIC,0.027 μg ml‐1) in that order. G‐MIC values ranging from 0.027–0.037 μg ml‐1 have been determined for itraconazole, econazole, amorolfine (RO 14–4767/002), miconazole and 5‐fluorocytosine. Among the orally active azole derivatives fluconazole was the least active (G‐MIC,0.14 μg ml‐1). Noteworthy activity included that of the allylamine terbinafine which was similar to that of bifonazole (G‐MIC 0.23–0.26 μg ml‐1). There was a statistically significant higher susceptibility of the test strains with terbinafine than with amphotericin B. Naftifine and amphotericin B were comparable active in terms of G‐MIC values (0.52–0.7 μg ml‐1). Significantly higher drug concentrations (> 1 μg ml‐1) were necessary to inhibit filamentation of C. albicans with ciclopiroxolamine, nystatin, griseofulvin and tolciclate. Tolnaftate was the least active drug tested with a G‐MIC of 74.7 μg ml‐1.