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Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-6205

Klaassen, T; Jetter, A; Tomalik-Scharte, D; Kasel, D; Kirchheiner, J; Jaehde, U; Fuhr, U (2008). Assessment of urinary mephenytoin metrics to phenotype for CYP2C19 and CYP2B6 activity. European Journal of Clinical Pharmacology, 64(4):387-398.

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OBJECTIVES: (S)-Mephenytoin is selectively metabolised to (S)-4'-hydroxymephenytoin by CYP2C19. The urinary excretion of 4'-hydroxymephenytoin reflects the activity of individual enzymes. We evaluated fractioned urinary collection and beta-glucuronidase pre-treatment in order to determine the optimal CYP2C19 metrics. We also assessed whether urinary excretion of N-desmethylmephenytoin (nirvanol) might be a useful CYP2B6 metric in in vivo studies. METHODS: A 50-mg dose of mephenytoin was administered to 52 volunteers as a component of phenotyping cocktails in four separate studies. Urine was collected up to 166 h post-dose. Urinary excretion of 4'-hydroxymephenytoin and nirvanol was quantified by liquid chromatography-tandem mass spectrometry, and common CYP2C19 and CYP2B6 genotypes were determined. RESULTS: Cumulative excretion of 4'-hydroxymephenytoin in urine with beta-glucuronidase treatment collected from before mephenytoin administration up to 12-16 h thereafter showed the greatest difference between CYP2C19 genotypes and the lowest intra-individual variability (7%). Renal elimination of nirvanol was highest for a *4/*4 individual and lowest for individuals carrying the *5/*5 and *1/*7 genotype, but lasted for several weeks, thus making its use in cross-over studies difficult. CONCLUSION: Cumulative urinary excretion of 4'-hydroxymephenytoin 0-12 h post-administration is a sensitive and reproducible metric of CYP2C19 activity, enabling the effect of a drug on CYP2C19 to be assessed in a small sample size of n=6 volunteers. While nirvanol excretion may reflect CYP2B6 activity in vivo, it is not useful for CYP2B6 phenotyping.

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Clinic for Clinical Pharmacology and Toxicology
DDC:610 Medicine & health
Date:April 2008
Deposited On:27 Nov 2008 11:46
Last Modified:27 Nov 2013 17:36
Additional Information:The original publication is available at www.springerlink.com
Publisher DOI:10.1007/s00228-007-0416-z
PubMed ID:18071681
Citations:Web of Science®. Times Cited: 3
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