Variability in the disposition of chlorzoxazone.
Chlorzoxazone is 6-hydroxylated by cytochrome P450 2E1 (CYP 2E1), which bioactivates many toxic and carcinogenic molecules. Seventeen volunteers of varying age, ethnicity, and gender received a 250 mg tablet of chlorzoxazone and their blood and urine were sampled frequently for 8 h. V/F = 42 +/- 21 L and CL/F = 412 +/- 120 mL min-1. Comparison of these values with a study by other investigators using a suspension dosage form suggested that relative Ftablet approximately 0.7. The fraction excreted in the urine as 6-hydroxychlorzoxazone (fe,6-OH) was 0.39 +/- 0.20 and that portion of the total CL accounted for by CYP 2E1-mediated metabolism (CL6-OH) was 163 +/- 95 mL min-1. Thus, while V/F and CL/F varied by factors of less than five, fe,6-OH varied 16-fold and CL6-OH varied 28-fold. These results suggested that there was considerable inter-individual variability in the metabolism of chlorzoxazone to 6-hydroxychlorzoxazone. This variability will significantly affect the construction of physiologically based pharmacokinetic models that use the 6-hydroxylation of chlorzoxazone as a marker for an individual's CYP 2E1 phenotype.
Department of Pharmacy, School of Pharmacy, University of California, San Francisco 94143-0446.
J D
JD
de Vries
L
L
Salphati
S
S
Horie
C E
CE
Becker
B A
BA
Hoener
D000284:Administration, Oral; D000328:Adult; D000428:Alcohol Drinking / Q000378:metabolism; D044466:Asian People; D044383:Black People; D001798:Blood Proteins; D002753:Chlorzoxazone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D019392:Cytochrome P-450 CYP2E1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005260:Female; D006801:Humans; D006900:Hydroxylation; D008297:Male; D008875:Middle Aged; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010641:Phenotype; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D044465:White People
D001798:Blood Proteins; C039289:6-hydroxychlorzoxazone; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating; D002753:Chlorzoxazone