Susceptibilities of clinical and laboratory isolates of Blastomyces dermatitidis to ketoconazole, itraconazole, and fluconazole

Eighteen isolates of Blastomyces dermatitidis were evaluated for their in vitro susceptibilities to ketoconazole, itraconazole, and fluconazole. The MIC ranges were 0.1 to 0.4 mu g/ml for ketoconazole, less than or equal to 0.018 to 0.07 mu g/ml for itraconazole, and 2.5 to 4.0 mu g/ml for fluconazole. The ranges for the minimal lethal concentrations were 0.2 to 0.8 mu g/ml for ketoconazole, less than or equal to 0.018 to 0.07 mu g/ml for itraconazole, and 10 to 40 mu g/ml for fluconazole. Itraconazole was the most active agent against B. dermatitidis in vitro, while fluconazole was the least active. These results correlate with the clinical efficacies noted to date with doses of these agents used to treat blastomycosis.