In vitro antifungal activity of clotrimazole (Bay b 5097)

The in vitro antifungal activity of clotrimazole (Bay b 5097) was compared with those of amphotericin B, griseofulvin, nystatin, and pyrrolnitrin. The inhibitory activity of clotrimazole against most systemic pathogens was comparable to that of amphotericin B; minimal inhibitory concentrations of the two drugs for Blastomyces dermatitidis, Histoplasma capsulatum, Sporothrix schenckii, Cryptococcus neoformans, and Coccidioides immitis were in the range of 0.20 to 3.13 and 0.10 to 6.25 mug/ml, respectively. One isolate of Allescheria boydii was resistant to 100 mug of amphotericin B per ml but was inhibited by 6.25 mug of clotrimazole per ml. Clotrimazole was less active than amphotericin B against Candida albicans and Aspergillus fumigatus. The activity of clotrimazole against dermatophytes was comparable to that of pyrrolnitrin; 0.78 mug of either compound per ml was fungicidal for most isolates of Trichophyton sp., Microsporum sp. and Epidermophyton floccosum. Both griseofulvin and nystatin were less active than clotrimazole. The size of inoculum was shown to have a significant effect on the results of in vitro susceptibility testing with clotrimazole.