title: Pharmacokinetics of triamcinolone acetonide following intramuscular and intra-articular administration to exercised Thoroughbred horses.
abstract: BACKGROUND
  The use of triamcinolone acetonide (TA) in performance horses necessitates establishing appropriate withdrawal times prior to performance.
  
  
  OBJECTIVE
  To describe the plasma pharmacokinetics of TA and time-related urine and synovial fluid concentrations following i.m. and intra-articular administration to exercised Thoroughbred horses.
  
  
  METHODS
  Block design.
  
  
  METHODS
  Twelve racing fit adult Thoroughbred horses received a single i.m. administration of TA (0.1 mg/kg bwt). After an appropriate washout period, the same horses then received a single intra-articular TA administration (9 mg) into the right antebrachiocarpal joint. Blood, urine and synovial fluid samples were collected prior to, and at various times, up to 60 days post drug administration and analysed using liquid chromatography-mass spectrometry. Plasma data were analysed using noncompartmental analysis.
  
  
  RESULTS
  Maximum measured plasma TA concentrations were 0.996 ± 0.391 at 13.2 h and 1.27 ± 0.278 ng/ml at 6.5 h for i.m. and intra-articular administration, respectively. The plasma terminal elimination half-life was 11.4 ± 6.53 and 0.78 ± 1.00 days for i.m. and intra-articular administration, respectively. Following i.m. administration, TA was below the limit of detection (LOD) by Days 52 and 60 in plasma and urine, respectively. Following intra-articular administration TA was undetectable by Day 7 in plasma and Day 8 in urine. Triamcinolone acetonide was also undetectable in any of the joints sampled following i.m. administration and remained above the limit of quantitation (LOQ) for 21 days following intra-articular administration.
  
  
  CONCLUSIONS
  This study extends previous studies describing the pharmacokinetics of TA following i.m. and intra-articular administration to the horse and suggests that plasma and urine concentrations are not a good indicator of synovial fluid concentrations. Furthermore, results of this study supports an extended withdrawal time for TA given i.m.
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, USA; Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, USA.
authors.forename: H K
authors.initials: HK
authors.lastname: Knych
authors.forename: M A
authors.initials: MA
authors.lastname: Vidal
authors.forename: H C
authors.initials: HC
authors.lastname: Casbeer
authors.forename: D S
authors.initials: DS
authors.lastname: McKemie
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D005260:Female; D006207:Half-Life; D006736:Horses / Q000378:metabolism*; D007270:Injections, Intra-Articular; D007273:Injections, Intramuscular; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D014222:Triamcinolone Acetonide / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D000893:Anti-Inflammatory Agents; D014222:Triamcinolone Acetonide
keywords: Thoroughbred; corticosteroid; horse; pharmacokinetics; syonvial fluid; triamacinolone acetonide (TA)