LAUSR

Isavuconazonium sulfate is a prodrug of isavuconazole, a broad-spectrum mould-active triazole antifungal drug. We provide a direct comparison of the in vitro activity of the prodrug versus the active metabolite against clinical isolates of Aspergillus spp., Sarocladium kiliense, and Scedosporium apiospermum using CLSI broth microdilution methods. The MIC values obtained for the prodrug were one 2-fold dilution higher than those of isavuconazole for all isolates tested. Using previously defined epidemiological cutoff values for isavuconazole and Aspergillus spp., 96.4% of isolates were wild type (WT) to isavuconazole and only 75% were WT to the prodrug. The essential agreement (±2 log2 dilutions) between prodrug and isavuconazole MIC values was 96.4% across all tested isolates. The active metabolite, isavuconazole, is recommended to use during in vitro susceptibility testing of fungal isolates.