title: Pharmacokinetics and tissue elimination of tulathromycin following subcutaneous administration in meat goats.
abstract: OBJECTIVE
  To determine the tissue depletion profile of tulathromycin and determine an appropriate slaughter withdrawal interval in meat goats after multiple SC injections of the drug.
  
  
  METHODS
  16 healthy Boer goats.
  
  
  METHODS
  All goats were administered tulathromycin (2.5 mg/kg, SC) twice, with a 7-day interval between doses. Blood samples were collected throughout the study, and goats were euthanized at 2, 5, 10, and 20 days after the second tulathromycin dose. Lung, liver, kidney, fat, and muscle tissues were collected. Concentrations of tulathromycin in plasma and the hydrolytic tulathromycin fragment CP-60,300 in tissue samples were determined with ultrahigh-pressure liquid chromatography-tandem mass spectrometry.
  
  
  RESULTS
  The plasma profile of tulathromycin was biphasic. Absorption was very rapid, with maximum drug concentrations (1.00 ± 0.42 μg/mL and 2.09 ± 1.77 μg/mL following the first and second doses, respectively) detected within approximately 1 hour after injection. Plasma terminal elimination half-life of tulathromycin was 61.4 ± 14.1 hours after the second dose. Half-lives in tissue ranged from 2.4 days for muscle to 9.0 days for lung tissue; kidney tissue was used to determine the withdrawal interval for tulathromycin in goats because it is considered an edible tissue.
  
  
  CONCLUSIONS
  On the basis of the tissue tolerance limit in cattle of 5 ppm (μg/g), the calculated withdrawal interval for tulathromycin would be 19 days following SC administration in goats. On the basis of the more stringent guidelines recommended by the FDA, the calculated meat withdrawal interval following tulathromycin administration in goats was 34 days.
authors.affiliation: Food Animal Residue Avoidance Databank, Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Romanet
authors.forename: Geof W
authors.initials: GW
authors.lastname: Smith
authors.forename: Teresa L
authors.initials: TL
authors.lastname: Leavens
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Baynes
authors.forename: Scott E
authors.initials: SE
authors.lastname: Wetzlich
authors.forename: Jim E
authors.initials: JE
authors.lastname: Riviere
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Tell
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000097:blood / Q000493:pharmacokinetics*; D004187:Disaccharides / Q000097:blood / Q000493:pharmacokinetics*; D005260:Female; D006041:Goats / Q000097:blood / Q000378:metabolism*; D006571:Heterocyclic Compounds / Q000097:blood / Q000493:pharmacokinetics*; D007279:Injections, Subcutaneous / Q000662:veterinary; D008297:Male; D053719:Tandem Mass Spectrometry / Q000662:veterinary; D013997:Time Factors; D014018:Tissue Distribution; D018942:Macrolides
chemical_list: D000900:Anti-Bacterial Agents; D004187:Disaccharides; D006571:Heterocyclic Compounds; C485204:tulathromycin; D018942:Macrolides