title: Comparison of pharmacokinetics of fentanyl after intravenous and transdermal administration in cats.
abstract: OBJECTIVE
  To compare pharmacokinetic and pharmacodynamic characteristics of fentanyl citrate after IV or transdermal administration in cats.
  
  
  METHODS
  6 healthy adult cats with a mean weight of 3.78 kg.
  
  
  METHODS
  Each cat was given fentanyl IV (25 mg/cat; mean +/- SD dosage, 7.19 +/- 1.17 mg/kg of body weight) and via a transdermal patch (25 microg of fentanyl/h). Plasma concentrations of fentanyl were measured by use of radioimmunoassay. Pharmacokinetic analyses of plasma drug concentrations were conducted, using an automated curve-stripping process followed by nonlinear, least-squares regression. Transdermal delivery of drug was calculated by use of IV pharmacokinetic data.
  
  
  RESULTS
  Plasma concentrations of fentanyl given IV decreased rapidly (mean elimination half-life, 2.35 +/- 0.57 hours). Mean +/- SEM calculated rate of transdermal delivery of fentanyl was 8.48 +/- 1.7 mg/h (< 36% of the theoretical 25 mg/h). Median steady-state concentration of fentanyl 12 to 100 hours after application of the transdermal patch was 1.58 ng/ml. Plasma concentrations of fentanyl < 1.0 ng/ml were detected in 4 of 6 cats 12 hours after patch application, 5 of 6 cats 18 and 24 hours after application, and 6 of 6 cats 36 hours after application.
  
  
  CONCLUSIONS
  In cats, transdermal administration provides sustained plasma concentrations of fentanyl citrate throughout a 5-day period. Variation of plasma drug concentrations with transdermal absorption for each cat was pronounced. Transdermal administration of fentanyl has potential for use in cats for long-term control of pain after surgery or chronic pain associated with cancer.
authors.affiliation: Department of Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Lee
authors.forename: M G
authors.initials: MG
authors.lastname: Papich
authors.forename: E M
authors.initials: EM
authors.lastname: Hardie
mesh_terms: D000287:Administration, Topical; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D019540:Area Under Curve; D002415:Cats / Q000378:metabolism*; D005283:Fentanyl / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D006207:Half-Life; D007275:Injections, Intravenous / Q000662:veterinary; D011863:Radioimmunoassay / Q000662:veterinary; D012044:Regression Analysis
chemical_list: D000701:Analgesics, Opioid; D005283:Fentanyl