Monitoring isavuconazole blood concentrations

Isavuconazole plasma concentration monitoring is not routinely recommended because data show that more than 90% of patients achieve a therapeutic trough concentration. Monitoring may be considered inAndes 2018McCreary 2023:

• patients with altered pharmacokinetics (eg patients with critical illness, obesity or advanced age)
• children
• patients taking medications that significantly interact with isavuconazole
• patients who need a modified formulation (eg opening capsulesAdamsick 2019Dieringer 2022)
• suspected toxicity
• therapeutic failure.

Isavuconazole has a long elimination half-life. Isavuconazole blood concentrations can be measured at any point during the dosing interval; however, trough concentrations are most commonly usedMcCreary 2023. Steady state is usual achieved 5 to 7 days after starting therapy when a loading dose is givenMcCreary 2023.

Data informing the target trough concentration for isavuconazole are limited. Some experts recommend a trough concentration of 1 mg/L to 5 mg/L to optimise efficacy and avoid toxicityMcCreary 2023. Concentrations above 5 mg/L are associated with hepatoxicityElhence 2022.

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