Therapeutic drug monitoring-guided high-dose isavuconazole therapy for invasive pulmonary aspergillosis in a patient on extracorporeal membrane oxygenation support

We review the case of a 58-year-old female on extracorporeal membrane oxygenation (ECMO) support diagnosed with invasive pulmonary aspergillosis (IPA). Intravenous isavuconazole was started, requiring dose escalation to achieve isavuconazole trough concentration (ISA-Cmin) within the therapeutic range (2.5-5.0 μg/mL). For more than 4 months, she maintained a dose of 200 mg q12h, with a median ISA-Cmin of 3.4 (interquartile range [IQR]: 3.1-4.9) µg/mL. Throughout this interval, 17 assessments of ISA-Cmin were performed (weekly). Of these, 82% (14/17) were within the therapeutic range, with an intra-individual variability of 36.8%. Although no signs of hepatotoxicity were observed, she experienced short-term gastrointestinal adverse events related to potential isavuconazole over-exposure (ISA-Cmin > 5.0 μg/mL). ECMO circuit changes did not appear to affect ISA-Cmin. She was not obese (IMC ≈ 25 kg/m²) and did not require other extracorporeal therapy, but hypoalbuminemia may have contributed to an increase in unbound isavuconazole fraction and consequently its clearance.