title: Therapeutic hypothermia-induced pharmacokinetic alterations on CYP2E1 chlorzoxazone-mediated metabolism in a cardiac arrest rat model.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Laboratory investigation.
  
  
  METHODS
  University pharmacy school and animal research facility.
  
  
  METHODS
  Sixteen male Sprague-Dawley rats.
  
  
  METHODS
  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 degrees C and 30 degrees C using control rat microsomes at varying concentrations of chlorzoxazone.
  
  
  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 degrees C and 30 degrees C, and CYP2E1 enzyme capacity (maximum velocity) was not altered at these different incubation temperatures. However, Michaelis-Menten constant was significantly increased at 30 degrees C (551+/-150 microM) compared with incubations at 37 degrees C (255+/-52 microM, 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.
authors.affiliation: University of Pittsburgh School of Pharmacy, Department of Pharmaceutical Sciences, and Department of Paediatrics, the Children't Hospital of Pittsburgh, PA, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Tortorici
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Kochanek
authors.forename: Robert R
authors.initials: RR
authors.lastname: Bies
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Poloyac
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D019540:Area Under Curve; D002753:Chlorzoxazone / Q000493:pharmacokinetics*; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism* / Q000493:pharmacokinetics; D006323:Heart Arrest / Q000628:therapy*; D007036:Hypothermia, Induced; D008297:Male; D008657:Metabolic Clearance Rate; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D019392:Cytochrome P-450 CYP2E1; D002753:Chlorzoxazone