title: Pharmacokinetic comparisons of tail-bleeding with cannula- or retro-orbital bleeding techniques in rats using six marketed drugs.
abstract: BACKGROUND
  The evaluation of drug disposition properties of chemical entities in drug discovery research typically involves the conduct of pharmacokinetic studies in rodents that requires blood sampling over several time points, preferably without disrupting the physiological status of the animals. Several blood withdrawal methods have been employed throughout the industry, yet these methods have not been comprehensively evaluated with regard to their effects on pharmacokinetic profiles of the drug investigated to recommend best practices.
  
  
  METHODS
  In this paper, the pharmacokinetics of six marketed drugs from four distinct therapeutic classes were compared using tail-vein, femoral-artery cannula-, and retro-orbital sinus bleeding techniques. The marketed drugs used in these studies were pentoxifylline, gemfibrozil, glipizide, methotrexate, clonidine, and fluoxetine.
  
  
  RESULTS
  Following oral administration, peak plasma concentration (C(max)), and area under the curve (AUC(0-24)) values for all compounds were not significantly different with the tail-vein method when compared to cannula- or retro-orbital sinus bleeding, except for fluoxetine and gemfibrozil for which minor, but statistically significant differences were observed. The effect of arterial versus venous tail-bleeding on the pharmacokinetics of pentoxifylline indicated no statistical differences in either C(max) or AUC(0-24) values. However, for fluoxetine, higher exposures were observed with tail arterial than venous sampling (2-fold with respect to C(max) and 1.7-fold with respect to AUC(0-24), p<0.05).
  
  
  CONCLUSIONS
  The observed differences with fluoxetine may be due to its pharmacological effects on thermoregulatory responses that influence tail blood flow, a hypothesis that remains to be tested. Based on these observations, we recommend the tail-bleeding technique for pharmacology or toxicology exposure and F% studies, particularly in early discovery work. Retro-orbital bleeding is controversial and is no longer considered a humane method. Cannula-bleeding, especially coupled with automated blood-collection techniques, has become the most efficient way for pharmaceutical industry to perform rat bioavailability studies.
authors.affiliation: Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, United States. yuhuahui@lilly.com
authors.forename: Yu-hua
authors.initials: YH
authors.lastname: Hui
authors.forename: Naijia Helen
authors.initials: NH
authors.lastname: Huang
authors.forename: Lewis
authors.initials: L
authors.lastname: Ebbert
authors.forename: Holly
authors.initials: H
authors.lastname: Bina
authors.forename: Alan
authors.initials: A
authors.lastname: Chiang
authors.forename: Carma
authors.initials: C
authors.lastname: Maples
authors.forename: Michael
authors.initials: M
authors.lastname: Pritt
authors.forename: Tom
authors.initials: T
authors.lastname: Kern
authors.forename: Nita
authors.initials: N
authors.lastname: Patel
mesh_terms: D000284:Administration, Oral; D000818:Animals; D019540:Area Under Curve; D001682:Biological Availability; D001800:Blood Specimen Collection / Q000379:methods; D002406:Catheterization, Peripheral / Q000379:methods*; D003000:Clonidine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D015507:Drugs, Investigational / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics*; D005473:Fluoxetine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D015248:Gemfibrozil / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D005913:Glipizide / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D006207:Half-Life; D007275:Injections, Intravenous; D008297:Male; D008727:Methotrexate / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D015394:Molecular Structure; D009915:Orbit / Q000098:blood supply*; D010431:Pentoxifylline / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D013623:Tail / Q000098:blood supply*; D013997:Time Factors
chemical_list: D015507:Drugs, Investigational; D005473:Fluoxetine; D003000:Clonidine; D015248:Gemfibrozil; D010431:Pentoxifylline; D005913:Glipizide; D008727:Methotrexate