Abstract
Voriconazole is a broad spectrum antifungal agent for treating life-threatening fungal infections. Its clearance is approximately 3-fold higher in children compared with adults. Voriconazole is cleared predominantly via hepatic metabolism in adults, mainly by CYP3A4, CYP2C19, and flavin-containing monooxygenase 3 (FMO3). In vitro metabolism of voriconazole by liver microsomes prepared from pediatric and adult tissues (n = 6/group) mirrored the in vivo clearance differences in children versus adults, and it showed that the oxidative metabolism was significantly faster in children compared with adults as indicated by the in vitro half-life (T1/2) of 33.8 ± 15.3 versus 72.6 ± 23.7 min, respectively. The Km for voriconazole metabolism to N-oxide, the major metabolite formed in humans, by liver microsomes from children and adults was similar (11 ± 5.2 versus 9.3 ± 3.6 μM, respectively). In contrast, apparent Vmax was approximately 3-fold higher in children compared with adults (120.5 ± 99.9 versus 40 ± 13.9 pmol/min/mg). The calculated in vivo clearance from in vitro data was found to be approximately 80% of the observed plasma clearance values in both populations. Metabolism studies in which CYP3A4, CYP2C19, or FMO was selectively inhibited provided evidence that contribution of CYP2C19 and FMO toward voriconazole N-oxidation was much greater in children than in adults, whereas CYP3A4 played a larger role in adults. Although expression of CYP2C19 and FMO3 is not significantly different in children versus adults, these enzymes seem to contribute to higher metabolic clearance of voriconazole in children versus adults.
Footnotes
This work was supported by the National Institutes of Health National Institute of Child Health and Human Development [Grant NCC-PPRU 5U10 HD045962-06]. D.K.B. was supported by the National Institutes of Health [Grants 1RO1-HD05795602, 1RO1-FD00351901, 1U10-HD4596206, 1K24-HD05873501, Government Contract HHSN267200700051C] (for work in pediatric and neonatal clinical pharmacology); the nonprofit organization Thrasher Research Foundation for work in neonatal candidiasis (http://www.thrasherresearch.org); and the industry for neonatal and pediatric drug development (http://www.dcri.duke.edu/research/coi.jsp).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.029769
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- FMO
- flavin-containing monooxygenase
- AUC
- area under the plasma concentration-time curve
- P450
- cytochrome P450
- HPLC
- high-performance liquid chromatography
- HPLC-MS/MS
- high-performance liquid chromatography coupled with tandem mass spectrometry
- CLint
- intrinsic clearance
- MPPG
- milligram microsomal protein per gram liver
- ƒu
- unbound fraction of drug.
- Received August 2, 2009.
- Accepted October 16, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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