Therapeutic Drug Monitoring of Oral Voriconazole in an Infant Less than Six Months of Age and Pharmacokinetics Changes Induced by Development of CYP2C19 in the Growth Process: A Novel Case Report.

Therapeutic drug monitoring (TDM) is recommended for voriconazole (VRCZ) to avoid adverse events and maximize antifungal efficacy. Currently, the appropriate dose for patients under the age of 2 years is unknown. Here, we report the case of a 1.5-month-old infant with inborn errors of immunity who was orally administered VRCZ. This patient's plasma concentration decreased significantly from 3.8 µg/mL (day 6) to 0.09 µg/mL (day 21), leading to repeated dose escalations to achieve the target concentration (1.38 µg/mL, day 58). The signal intensity ratio of VRCZ to its main metabolite, N-oxide VRCZ, in LC/MS/MS also decreased from 5.30 (day 6) to 0.57 (day 64). Consequently, we suspected that VRCZ metabolism may be enhanced during infant growth. To our knowledge, this is the first report of remarkable changes in VRCZ pharmacokinetics with metabolic activity enhanced by the growth process. In conclusion, we propose that frequent TDM helped to maintain adequate VRCZ plasma concentration in a infants less than 6 months of age.