Isavuconazole: Need for therapeutic drug monitoring and CYP polymorphism testing

In this patient of invasive sinusitis due to Rhizopus arrhizus, Therapeutic drug monitoring (TDM) showed a high trough level (88mg/L) of isavuconazole on standard doses. Genotyping revealed CYP3A5∗3/∗3 polymorphism which indicated poor metabolism of isavuconazole. Switching to posaconazole was attempted but there was intolerance to posaconazole. To our knowledge, this is the first patient in whom both TDM and CYP genotyping were used to plan very low and infrequent doses of isavuconazole.