Concentrations of dexmedetomidine and effect on biomarkers of cartilage toxicity following intra-articular administration in horses

OBJECTIVEThe goal of this study was to determine plasma, urine, and synovial fluid concentrations and describe the effects on biomarkers of cartilage toxicity following intra-articular dexmedetomidine administration to horses.ANIMALS12 research horses.PROCEDURESHorses received a single intra-articular administration of 1 kig/kg or 5 kig/kg dexmedetomidine or saline. Plasma, urine, and synovial fluid were collected prior to and up to 48 hours postadministration, and concentrations were determined. The effects on CS846 and C2C were determined in synovial fluid at 0, 12, and 24 hours postadministra- tion using immunoassays.RESULTSPlasma concentrations of dexmedetomidine fell below the limit of quantification (LOQ) (0.005 ng/mL) by 2.5 and 8 hours postadministration of 1 and 5 kig/kg, respectively. Synovial fluid concentrations were above the LOQ (0.1 ng/mL) of the assay at 24 hours in both dose groups. Drug was not detected in urine samples at any time post -drug administration. CS846 concentrations were significantly decreased relative to baseline at 12 hours postadmin- istration in the saline group and significantly increased in the 5-kig/kg-dose group at 24 hours. Concentrations of C2C were significantly decreased at 12 and 24 hours postadministration in the saline treatment group. There were no significant differences in CS846 or C2C concentrations between dose groups at any time. CLINICAL RELEVANCESystemic concentrations of dexmedetomidine remained low, compared to synovial fluid concentrations. CS846, a marker of articular cartilage synthesis, increased in a dose-dependent fashion. Based on these findings, further dose titration and investigation of analgesic and adverse effects are warranted.