Evaluation of voriconazole therapeutic drug monitoring in malignant hematology patients

Introduction Malignant hematology (MH) patients are susceptible to invasive fungal infections due to prolonged neutropenia and immunosuppressive therapies, which may require voriconazole therapy. Although voriconazole therapeutic drug monitoring (TDM) is common, evidence describing this practice is limited. The primary objective of this study was to describe the current practice of voriconazole TDM in MH patients at the Princess Margaret Cancer Centre (PM). Methods A retrospective chart review was conducted for MH inpatients initiated on voriconazole at PM between November 1st, 2019 and November 13th, 2020. Data regarding voriconazole doses, levels, dose changes, and adverse effects were collected. The primary endpoint was the proportion of patients with initial voriconazole levels within therapeutic range (1–5 mg/L). Results Fifty-six patients were included in the study. The most common reason for starting voriconazole was possible invasive fungal infection (44 patients, 78.6%). Fifty-one patients (91.1%) received a loading dose of voriconazole, averaging 386.5 ± 78.5 mg. The average maintenance dose was 242.1 ± 45.7 mg. An average of 2.6 ± 2.9 levels were drawn per patient with an average level of 3.2 ± 2.4 mg/L. Forty-one patients (73.2%) had an initial voriconazole level within therapeutic range and 90 out of 145 total levels (62.1%) were within therapeutic range. There were 52 dose modifications made; 31 (60.8%) doses adjusted, 12 (23.5%) doses held, and 9 (17.6%) doses discontinued. For the 31 dose adjustments, 26 (83.9%) had a level redrawn and 17 (65.4%) of those levels were within therapeutic range. Twenty-three (41.1%) patients developed adverse effects, 8 (34.8%) of which were associated with supratherapeutic levels. Of these 23 patients, 19 (33.9%) experienced transaminitis, 3 (5.4%) experienced both transaminitis and neurotoxicity, and 1 (1.8%) experienced photopsia. Conclusion Overall, 41 (73.2%) patients achieved an initial voriconazole level within therapeutic range. Of these 41 patients, 30 (73.2%) remained within therapeutic range for the duration of their inpatient voriconazole therapy. These findings suggest that the current practice of voriconazole TDM at our institution is yielding largely positive results, but still has room for improvement.