Real-world Experience of Posaconazole Therapeutic Drug Monitoring in Oncology Patients: Clinical Implications of Hypoalbuminemia as a Predictor of Subtherapeutic Posaconazole Levels.

Background: Posaconazole maintains broad antifungal activity and is employed for prevention and treatment of invasive fungal infections in oncology patients. Older formulations required therapeutic drug monitoring, and specific plasma drug levels have been recommended. This study evaluated factors associated with subtherapeutic concentrations with the newer delayed-release tablet formulation. Methods: In this retrospective, single-center cohort study at a national comprehensive cancer center, all oncology patients receiving delayed-release posaconazole at standard dosing of 300 mg orally per day from 06/2021 to 07/2023 with plasma drug concentration evaluation were identified. Demographic, clinical, and laboratory data were evaluated to identify risk factors associated with subtherapeutic drug levels at targets of ≥1.25 µg/mL and ≥1.8 µg/mL. Results: Of 110 patients identified, 98 met criteria for inclusion in the study. The median time from initiation of posaconazole to drug level assessment was 13 days, and the median concentration was 1.29 µg/mL. Of the 22 patients receiving posaconazole for prophylaxis, 5 (22.7%) failed to achieve concentrations ≥0.7 µg/mL, and of 76 patients receiving posaconazole for treatment, 38 (50%) failed to achieve concentrations of ≥1.25 µg/mL. In multivariable analysis, albumin of ≤3 g/dL and ideal body weight ≥60 kg were found to be associated with subtherapeutic levels. For a higher target of ≥1.8 µg/mL, only albumin ≤3 g/dL was associated with subtherapeutic levels for the variables evaluated. Conclusions: A higher initial dosing strategy and therapeutic drug monitoring for oncology patients with albumin ≤3 g/dL receiving posaconazole, particularly for the treatment of invasive fungal infection, could be considered.