In Vitro Antifungal Activity of Isavuconazole against 345 Mucorales Isolates Collected at Study Centers in Eight Countries

Although mucormycoses (formerly zygomycoses) are relatively uncommon, they are associated with high mortality and treatment options are limited. Isavuconazole is a novel, water soluble, broad-spectrum azole in clinical development for the treatment of invasive aspergillosis and candidiasis. The objective of this report was to collate data on the in vitro activity of isavuconazole against a collection of 345 diverse Mucorales isolates, collected and tested at eight study centers in Europe, Mexico and North America. Each study center undertook minimum inhibitory concentration (MIC) susceptibility testing of their isolates, according to EUCAST or CLSI guidelines. Across all study centers, isavuconazole exhibited MIC50 values of 1-4 mg/L and MIC90 values of 4-16 mg/L against the five genera. There were also marked differences in MIC distributions, which could be ascribed to differences in inoculum and/or endpoint. EUCAST guidelines appeared to generate modal MICs 2-fold higher than CLSI. These results confirm that isavuconazole possesses at least partial antifungal activity against Mucorales.