Voriconazole is extensively metabolized by the CYP450 isoenzymes 2C19 and 3A4 and to a lesser extent by CYP2C9; therefore, any medication that affects this pathway can alter its plasma concentration. Treatment failure can probably occur if subtherapeutic levels are achieved.

A 32-year-old woman who suffered from acute lymphoblastic leukemia was admitted and received treatment with vincristine and dexamethasone. After several days, to control her fever, based on two consecutive positive serum galactomannan test results, voriconazole as an antifungal agent was added to Aspergillus infection treatment. Through the first week after voriconazole initiation, its plasma concentrations were subtherapeutic. The most suspicious medication for interaction was dexamethasone, which can induce CYP450 isoenzymes and reduce plasma concentration.

As a result of the narrow therapeutic window of voriconazole and the relationship between efficacy and plasma concentration of azoles, therapeutic drug monitoring of voriconazole in patients receiving a high dose of glucocorticoids is recommended, in order to achieve optimal response to treatment and toxicity reduction. Further studies regarding the interaction between voriconazole and dexamethasone to prevent clinically relevant interactions should be considered.