Therapeutic hypothermia-induced pharmacokinetic alterations on CYP2E1 chlorzoxazone-mediated metabolism in a cardiac arrest rat model

Michael A. Tortorici, Patrick M. Kochanek, Robert R. Bies, Samuel M. Poloyac

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Objectives: Therapeutic hypothermia has demonstrated considerable benefit in patients experiencing cardiac arrest. Despite increasing clinical use, there is a paucity of information regarding the effect of hypothermia on the disposition of medications, specifically cytochrome P450-mediated drug metabolism. The objective was to determine the effect of hypothermia after cardiac arrest on the in vivo kinetics of a cytochrome P450 (CYP2E1) probe drug, chlorzoxazone, and to investigate the mechanism of these alterations. Design: Laboratory investigation. Setting: University pharmacy school and animal research facility. Subjects: Sixteen male Sprague-Dawley rats. Interventions: An asphyxial arrest rat model was used and moderate hypothermia was induced immediately postinsult via surface cooling. Chlorzoxazone was administered as an intravenous bolus, and plasma concentrations were analyzed using high-performance liquid chromatography methods. Protein binding was analyzed using rat control plasma, and Michaelis-Menten enzyme kinetic analysis was performed at 37°C and 30°C using control rat microsomes at varying concentrations of chlorzoxazone. Measurements and Main Results: Moderate hypothermia after cardiac arrest in rats markedly decreased the systemic clearance of the CYP2E1 substrate, chlorzoxazone, when compared with normothermia after cardiac arrest, 1.26 ± 0.34 mL/min vs. 0.580 ± 0.37 mL/min (p < .001). No changes in chlorzoxazone protein binding were observed at 37°C and 30°C, and CYP2E1 enzyme capacity (maximum velocity) was not altered at these different incubation temperatures. However, Michaelis-Menten constant was significantly increased at 30°C (551 ± 150 μM) compared with incubations at 37°C (255 ± 52 μM, p < .01). Conclusions: Moderate hypothermia markedly reduces the systemic clearance of chlorzoxazone in cardiac arrest rats. This results from hypothermia-induced decreases in the CYP2E1 enzyme affinity for the substrate chlorzoxazone. This is the first systematic mechanistic investigation of the effect of hypothermia on CYP2E1-mediated metabolism.

Original languageEnglish (US)
Pages (from-to)785-791
Number of pages7
JournalCritical care medicine
Issue number3
StatePublished - Mar 2006


  • CYP2E1
  • Cardiac arrest
  • Chlorzoxazone
  • Drug metabolism
  • Hypothermia
  • Pharmacokinetics

ASJC Scopus subject areas

  • Critical Care and Intensive Care Medicine

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