Isavuconazole therapeutic drug monitoring in real-world clinical practice: an age-stratified analysis of determinants

Objectives Although therapeutic drug monitoring (TDM) for isavuconazole (ISA) is not routinely recommended, its utility in specific populations remains debated. This study aimed to elucidate the need for ISA TDM and to identify the specific patient groups who might benefit from it. Methods We retrospectively analyzed 48 patients (13 pediatric, 19 non-elderly, 16 elderly) who underwent ISA TDM. Clinical characteristics, TDM results, dose adjustments, and outcomes were collected. Results A total of 179 trough measurements were obtained. Pediatric patients had a lowest median C trough of 2.6 mg/L and the highest interindividual variability (51.6%), particularly lower-weight pediatric patients were at an increased risk of underexposure. The median ISA C trough was significantly lower in elderly compared to non-elderly patients (2.9 vs. 4.3 mg/L, P < 0.001). TDM led to 21 dosage adjustments and substantial proportion of patients had C trough outside the therapeutic range (2–5 mg/L): 46.7% of pediatric patients, 48.9% of non-elderly patients, and 36.5% of elderly patients. Female sex, Intensive Care Unit (ICU) admission, and renal replacement therapy (RRT) were associated with lower levels in elderly patients. Conclusion TDM helps optimize dosing, especially in populations with high variability such as pediatric patients. Female sex, ICU admission, and RRT are important factors associated with lower exposure in elderly patients.