Pharmacokinetics of a Cytochrome P450 2E1 Probe, Chlorzoxazone, and its 6-Hydroxy Metabolite in Poloxamer 407-Induced Hyperlipidemic Rats

PURPOSE: To evaluate the possible changes in CYP2E1 expression and activity in hyperlipidemia (HL), we evaluated the pharmacokinetics of chlorzoxazone (CZX) as a CYP2E1 probe in rats with HL induced by poloxamer 407 (HL rats). METHODS: The pharmacokinetics of CZX and its 6-hydroxy metabolite (OH-CZX) were evaluated after intravenous administration of 20 mg/kg CZX to both control and HL rats. We also examined changes in the expression of CYP2E1 and its in vitro metabolic activity in hepatic microsomal fractions from HL rats. RESULTS: The total area under the plasma concentration-time curve (AUC) of CZX in the HL rats after its intravenous administration was comparable with that in the controls due to unchanged non-renal clearance (CLNR). The AUC of OH-CZX and AUCOH-CZX/AUCCZX ratios in HL rats also remained unchanged. This was primarily due to the comparable hepatic CLint for metabolism of CZX to OH-CZX via CYP2E1 between the control and HL rats as a result of unchanged expression of CYP2E1 in HL rats. CONCLUSIONS: This is the first study to evaluate CYP2E1 expression and activity in HL rats and their effects on the pharmacokinetics of a CYP2E1 probe drug. These findings have potential therapeutic implications assuming that the HL rat model qualitatively reflects similar changes in patients with HL.