title: Blood concentrations of remifentanil during and after infusion in horses anesthetized with isoflurane and dexmedetomidine.
abstract: OBJECTIVE
  To determine blood remifentanil concentration in isoflurane-anesthetized horses during and after a 1h remifentanil and dexmedetomidine infusion.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Six adult mixed breed horses with (mean±SD) bodyweight of 507±61kg and 14±4years of age.
  
  
  METHODS
  Following sedation with xylazine IV, anesthesia was induced with ketamine IV mixed with diazepam IV. Anesthesia was maintained with isoflurane in oxygen. After 52±7min for instrumentation, dexmedetomidine (0.25μgkg(-1) followed by 1.0μg(-1)kg(-1)h(-1)) and remifentanil infusions (6μgkg(-1)h(-1)) were administered for a minimum of 60min and horses recovered from anesthesia. Drug infusions were administered into the left jugular vein. Blood was sampled (4mL) from the right jugular vein at predefined intervals before and during administration of remifentanil infusion. Following catheter flush, blood was sampled from the left jugular vein after the infusion was terminated while the horse was recovering from anesthesia. Blood was placed into tubes containing sodium heparin with citric acid, flash frozen in liquid nitrogen, and stored at -80°C until analysis. Blood remifentanil concentration was measured using high performance liquid chromatography and tandem mass spectrometry.
  
  
  RESULTS
  Mean peak remifentanil concentration was 7.14ηgmL(-1) at 50min after start of infusion. Mean volume of distribution was 268±40mLkg(-1) and mean half-life was 12.8min. Blood concentration decreased to 1ηgmL(-1) 27min after termination of infusion. Limit of quantification was 0.2ηgmL(-1).
authors.affiliation: Department Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: Perrine
authors.initials: P
authors.lastname: Benmansour
authors.affiliation: College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Billinsky
authors.affiliation: Department Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada. Electronic address: tad551@mail.usask.ca.
authors.forename: Tanya
authors.initials: T
authors.lastname: Duke-Novakovski
authors.affiliation: College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: Jane
authors.initials: J
authors.lastname: Alcorn
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics* / Q000494:pharmacology; D000818:Animals; D020927:Dexmedetomidine / Q000493:pharmacokinetics* / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D006207:Half-Life; D006736:Horses / Q000097:blood / Q000378:metabolism* / Q000502:physiology; D007530:Isoflurane / Q000493:pharmacokinetics* / Q000494:pharmacology; D007649:Ketamine / Q000494:pharmacology; D008297:Male; D010880:Piperidines / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D000077208:Remifentanil; D014991:Xylazine / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D010880:Piperidines; D014991:Xylazine; D020927:Dexmedetomidine; D007649:Ketamine; D007530:Isoflurane; D000077208:Remifentanil; D003975:Diazepam
keywords: Dexmedetomidine; Horse; Infusion; Isoflurane; Remifentanil concentration