Clinical usefulness of therapeutic drug monitoring of voriconazole in a university hospital.

Introduction: The aim of this study was to assess the clinical usefulness of therapeutic drug monitoring (TDM) of voriconazole (VOR) in a university hospital.

Methods: A retrospective review was conducted on the clinical records of 52 patients treated with VOR and on whom TDM was performed. Steady-state trough plasma VOR concentration was measured at least 5 days after starting treatment. The therapeutic range of plasma VOR concentration was defined as 1-5.5μg/mL.

Results: The most frequent underlying conditions in the study population were lung transplant (48.1%) and hematological malignancies (26.9%). At the first TDM in each patient, VOR levels were outside the therapeutic range in 16 (30.7%) cases: <1μg/mL in 10 (19.2%) and >5.5μg/mL in 6 (11.5%). Eleven patients (21.2%) experienced severe muscle weakness and had considerable difficulty walking. All these patients were receiving concomitant treatment with corticosteroids. Age younger than 30 years (p=.005) and cystic fibrosis as the underlying disease (p=.04) were factors associated with low VOR levels. Almost all patients who had VOR concentrations >1μg/mL at the first TDM had a successful outcome (96%).

Conclusions: Plasma VOR concentrations were outside the therapeutic range at the first TDM in 30% (16/52) of patients. Age younger than 30 years and cystic fibrosis were factors associated with low VOR levels. The potential interactions between corticosteroids and VOR should be highlighted, as they could be responsible for a high rate of muscle weakness observed in our patients. Prospective trials are needed to investigate VOR TDM and corticosteroid pharmacokinetics.