Clinical and demographic factors affecting trough levels of isavuconazole in critically ill patients with or without COVID-19.

BACKGROUND: The broad-spectrum antifungal isavuconazole is administered to treat invasive aspergillosis and mucormycosis. OBJECTIVES: Isavuconazole plasma concentrations in critically ill ICU patients with or without COVID-19 and invasive fungal infection were determined, and factors for sub-therapeutic drug levels (<1 µg/mL) were evaluated. PATIENTS AND METHODS: Isavuconazole plasma levels were measured as part of therapeutic drug monitoring (TDM) in ICUs of a tertiary hospital. Concentrations determined 20-28 h after previous dosing were defined as trough (Cmin ) levels. A total of 160 Cmin levels from 62 patients with invasive fungal infections were analysed, 30 of which suffering from COVID-19. Patient characteristics included into univariable and multivariable analyses were gender, age, COVID-19 status, body mass index (BMI), sepsis-related organ failure (SOFA) score, renal replacement therapy (RRT) and extracorporeal membrane oxygenation (ECMO) requirement. RESULTS: The mean Cmin of isavuconazole in all patients was 1.64 µg/mL (interquartile range 0.83-2.24 µg/mL, total range 0.24-5.67 µg/mL). In total, 34.4% of the Cmin values (corresponding to 46.8% of patients) were below a threshold concentration of 1 µg/mL. Drug concentrations between patients with or without COVID-19 did not differ (p = .43). In contrast, levels were significantly lower in patients with female sex (p = .0007), age ≤ 65 years (p = .002), BMI > 25 (p = .006), SOFA score > 12 (p = .026), RRT (p = .017) and ECMO requirement (p = .001). CONCLUSIONS: Isavuconazole plasma levels can be negatively affected by patients' risk factors, supportive renal replacement and ECMO therapy. Future prospective studies analysing the relevance of isavuconazole drug levels in ICU patient outcome are urgently needed.

Isavuconazole therapeutic drug monitoring in critically ill ICU patients: A monocentric retrospective analysis.

BACKGROUND: The broad-spectrum triazole isavuconazole is used for the treatment of invasive aspergillosis and mucormycosis. Data regarding human plasma concentrations in clinical routine of the drug are rare. OBJECTIVES: Plasma concentrations of isavuconazole were determined in critically ill ICU patients while considering different patients' characteristics. METHODS: Retrospective analysis of isavuconazole plasma concentrations were obtained as part of routine therapeutic drug monitoring (TDM) of ICU patients with invasive aspergillosis or other fungal infections treated with isavuconazole. Plasma levels 0-4 h after last dosing were defined as peak levels (Cmax ), those 20-28 h after last dosing as trough levels (Cmin ). RESULTS: Overall, 223 isavuconazole levels of 41 patients were analysed, divided into 141 peak levels and 82 trough levels. The overall median Cmax was 2.36 µg/ml (mean 2.43 µg/ml, range 0.41-7.79 µg/ml) and the overall median Cmin was 1.74 µg/ml (mean 1.77 µg/ml, range 0.24-4.96 µg/ml). In total, 31.7% of the Cmin values of the total cohort were below the plasma target concentrations of 1 µg/ml, defined as EUCAST antifungal clinical breakpoint for Aspergillus fumigatus. Both peak and trough plasma levels of isavuconazole were significantly lower among patients with a body mass index (BMI) ≥25. In addition, a significant correlation was observed between isavuconazole trough levels and sepsis-related organ failure assessment (SOFA) score. CONCLUSIONS: This study shows that isavuconazole plasma concentrations vary in critical ill ICU patients. Significantly lower isavuconazole levels were associated with elevated BMI and higher SOFA score indicating a need of isavuconazole TDM in this specific patient population.