Broad-spectrum azoles and flucloxacillin: a dangerous match

Both invasive fungal infection with Aspergillus fumigatus and blood stream infection with methicillin-susceptible Staphylococcus aureus (MSSA) have a significant incidence in the critically ill. Voriconazole and, more recently, isavuconazole and high dose flucloxacillin are the standard first line treatments for these respective serious infections. However, an underestimated risk of a significant interaction needs to be taken into consideration, when both co-occur. We wish to highlight this important issue in the management of these patients through two case reports and to point to the inconsistency between different validated databases regarding this significant interaction as well the importance of a strict protocol for readily available therapeutic drug monitoring.