Treatment options and challenges for IAPA in the ICU
First-line treatment options for IPA include voriconazole and isavuconazole [35, 43]. Other options include echinocandins in combination with anti-mold azoles, and liposomal amphotericin B (L-AmB) in regions with high rates of azole-resistant A. fumigatus, although clinical data with L-AmB in ICU patients are limited [43, 44]. Achieving adequate drug exposure is challenging in ICU patients with multiple factors contributing to pharmacokinetic variability. Unlike L-AmB and the echinocandins, drug interactions are clinically relevant for the azoles and pharmacogenetic factors are important in inter-individual drug exposure variability [45]. The impact of therapeutic drug monitoring (TDM) for voriconazole shows a clear relation between exposure and both efficacy and toxicity. Target plasma trough voriconazole concentrations of ≥ 1.5–2 mg/L are associated with near-maximal clinical response in treatment of IA with a wild-type phenotype [46–51], with higher exposures (> 5.5 mg/L) increasing the risk of (neuro)toxicity. Higher trough concentrations (> 2 mg/L) are recommended for treatment of pathogens with elevated MICs (e.g., > 0.25 mg/L) [52]. For isavuconazole, there is no robust target plasma concentration, and the population average exposure of participants that demonstrated a favorable response (2–4 mg/L) is commonly used [43].