BACKGROUND Isavuconazole is a triazole antifungal drug, approved for the treatment of invasive aspergillosis and mucormycosis. It has been previously reported that an interaction between flucloxacillin and voriconazole may lead to subtherapeutic voriconazole exposure, when used concomitantly. Since isavuconazole is also metabolized via cytochrome P450 enzymes, the same interaction may be expected. OBJECTIVES We aim to document exposure to isavuconazole in patients concomitantly treated with flucloxacillin. PATIENTS We report two patients treated with both isavuconazole and flucloxacillin, in whom we determined isavuconazole concentrations. RESULTS Low isavuconazole trough concentrations (< 1 mg/L) were observed in two patients under concomitant treatment with flucloxacillin. CONCLUSIONS In combination with flucloxacillin, low isavuconazole concentrations were observed but an adequate isavuconazole exposure may be reached with dose augmentation. Therapeutic drug monitoring of isavuconazole is recommended to ensure an adequate exposure.
Interaction between flucloxacillin and azoles: is isavuconazole next?