The practice of intra-articular (IA) triamcinolone acetonide (TACA) injections is prevalent throughout horse racing. While urinary excretion of TACA administered IA in the fetlock and antebrachiocarpal joint has been described, there are no reports on urinary excretion when TACA is administered IA to the femoropatellar joint.
Ten geldings (mean age: 6.8 ± 1.8 years; mean bodyweight 559.0 ± 41.2 kg) received an IA injection of 18 mg (0.032 ± 0.002 mg/kg, 3 mL) TACA in the femoropatellar (stifle) joint. On Day 1, five geldings were injected into the left stifle joint, with the remaining five geldings injected into the right stifle joint the following day.
Urine was collected prior to treatment and 2 h post-administration then bihourly to 12 h. Samples were obtained every 12 h to 72 h then daily to 216 h post-administration. Samples were analysed for TACA, the metabolite 6β-hydroxy-TACA (6βOH-TACA) and endogenous hydrocortisone (HC) by HPLC-MS/MS, using both hydrolysed and unhydrolysed urine.
HC concentrations dropped in all horses by 4 h post-administration. By 6 h, no HC was detectable in any horse’s urine. This continued to 144 h post-administration where HC was detected in 4 out of 10 horses. At the end of the study there were still two horses with no detectable HC in urine.
Both TACA and 6βOH-TACA were present in all samples by 2 h post-administration and above LOQ in all horses for 60 h. At 216 h, six horses had urinary TACA concentrations above LOD. Only two horses had urine concentrations above the LOD for 6βOH-TACA at this time. One horse had urinary TACA and 6βOH-TACA concentrations above LOQ for the duration of the study. It would have returned a positive swab despite 8-day clear days post-treatment. These results were consistent between hydrolysed and unhydrolysed urine samples.