• Michael J Dolton, Gerd Mikus, Johanna Weiss, John E Ray, and Andrew J McLachlan.
• Faculty of Pharmacy, University of Sydney, Camperdown, Australia Centre For Education and Research on Ageing, Concord Repatriation General Hospital, Concord, Australia.
• J. Antimicrob. Chemother. 2014 Jun 1; 69 (6): 1633-41.

ObjectivesVoriconazole exhibits highly variable, non-linear pharmacokinetics and is associated with a narrow therapeutic range. This study aimed to investigate the population pharmacokinetics of voriconazole in adults, including the effect of CYP2C19 genotype and drug-drug interactions.MethodsNon-linear mixed effects modelling (NONMEM) was undertaken of six voriconazole studies in healthy volunteers and patients. Dosing simulations to examine influential covariate effects and voriconazole target attainment (2-5 mg/L) stratified by CYP2C19 phenotype were performed.ResultsWe analysed 3352 voriconazole concentration measurements from 240 participants. A two-compartment pharmacokinetic model with first-order oral absorption with lag time and Michaelis-Menten elimination best described voriconazole pharmacokinetics. Participants with one or more CYP2C19 loss-of-function (LoF) alleles had a 41.2% lower Vmax for voriconazole. Co-administration of phenytoin or rifampicin, St John's wort or glucocorticoids significantly increased voriconazole elimination. Among patients receiving 200 mg of voriconazole twice daily, predicted trough concentrations on day 7 were <2 mg/L for oral and intravenous regimens for 72% and 63% of patients without CYP2C19 LoF alleles, respectively, with 49% and 35% below this threshold with 300 mg twice daily dosing. Conversely, these regimens resulted in 29%, 39%, 57% and 77% of patients with CYP2C19 LoF alleles with voriconazole trough concentrations ≥5 mg/L.ConclusionsCurrent dosing regimens for voriconazole result in subtherapeutic exposure in many patients without CYP2C19 LoF alleles, suggesting the need for higher doses, whereas these regimens result in supratherapeutic exposure in a high proportion of patients with reduced CYP2C19 activity. These findings support the essential role of therapeutic drug monitoring in ensuring efficacious and safe voriconazole exposure.© The Author 2014. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

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