title: Effects of cysteine on the pharmacokinetics of intravenous chlorzoxazone in rats with protein-calorie malnutrition.
abstract: The effects of cysteine on the pharmacokinetics of chlorzoxazone (CZX) and one of its metabolites, 6-hydroxychlorzoxazone (OH-CZX), were investigated after intravenous administration of CZX, 25 mg/kg, to control rats (4-week fed on 23% casein diet) and rats with PCM (4-week fed on 5% casein diet) and PCMC (PCM with oral cysteine supplementation, 250 mg/kg, twice daily during the fourth week). In rats with PCM, the area under the plasma concentration-time curve from time zero to time infinity (AUC) of OH-CZX (436 compared with 972 microgmin/ml) and the percentages of intravenous dose of CZX excreted in 8-h urine as OH-CZX (20.2 compared with 38.5%) were significantly smaller than those in control rats. The above data indicated that the formation of OH-CZX from CZX decreased significantly in rats with PCM due to a significant decrease in chlorzoxazone-6-hydroxylase activity (328 compared with 895 pmol/min/mg protein) in the rats. The results were expected since in rats with PCM, hepatic CYP2E1 expression and its mRNA levels decreased significantly as compared to control, and CZX was metabolized to OH-CZX primarily by CYP2E1 in rats. By cysteine supplementation (rats with PCMC), some pharmacokinetic parameters restored fully (hepatic microsomal chlorzoxazone 6-hydroxylation activity based on both mg protein and nmol CYP450) or partially (total body clearance and apparent volume of distribution at steady state of CZX, and AUC, terminal half-life and 8-h urinary excretion of OH-CZX) to control levels.
authors.affiliation: College of Pharmacy, Research Institute of Pharmaceutical Sciences, Seoul National University, Kwanak-Gu, Republic of Korea.
authors.forename: Yoon G
authors.initials: YG
authors.lastname: Kim
authors.forename: Min K
authors.initials: MK
authors.lastname: Cho
authors.forename: Jong W
authors.initials: JW
authors.lastname: Kwon
authors.forename: Sang G
authors.initials: SG
authors.lastname: Kim
authors.forename: Suk J
authors.initials: SJ
authors.lastname: Chung
authors.forename: Chang-K
authors.initials: CK
authors.lastname: Shim
authors.forename: G
authors.initials: G
authors.lastname: Le Myung
mesh_terms: D000818:Animals; D019540:Area Under Curve; D002753:Chlorzoxazone / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D003545:Cysteine / Q000494:pharmacology*; D004435:Eating / Q000187:drug effects; D007275:Injections, Intravenous; D008297:Male; D009929:Organ Size / Q000187:drug effects; D011502:Protein-Energy Malnutrition / Q000097:blood / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution / Q000187:drug effects / Q000502:physiology; D015430:Weight Gain / Q000187:drug effects
chemical_list: D002753:Chlorzoxazone; D003545:Cysteine