Monitoring itraconazole blood concentrations

The absorption of itraconazole is unpredictable, and the bioavailability of available formulations varies. Monitor itraconazole plasma concentration when treating or preventing invasive fungal infections in immunocompromised patients (especially children).

Itraconazole has a long elimination half-life, so the concentration is best measured at least 5 days after starting therapy. For patients who did not receive a loading dose of itraconazole, steady state may not be reached until after 14 days of therapy. For treatment regimens, a trough concentration of 1 to 4 mg/L is appropriateChau 2021. For prophylaxis regimens, a trough concentration of 0.5 to 4 mg/L has been associated with improved outcomesChau 2021. Toxicity (eg fluid retention, gastrointestinal intolerance) has been reported with concentrations of more than 17 mg/LAbdul-Aziz 2020Cartledge 1997Chau 2021Denning 1994John 2019Lestner 2009Sharkey 1991Ullmann 2018.

For information on itraconazole plasma concentration monitoring in haematology patients, see the Australian and New Zealand antifungal consensus guidelines.