Poster Presentation 24th International Conference of Racing Analysts and Veterinarians 2026

Determination of the pharmacokinetics of triamcinolone acetonide administered intra-articularly to the femoropatellar joint of the horse. (130271)

Glenys K Noble 1 , Raf Labens 1 , Jaymie Loy 1 , Colin J Scrivener 1 , Himasha Mendis 2 , David Batty 2 , Adam Cawley 2
  1. School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
  2. Racing Analytical Services Ltd, Flemington, Victoria, Australia

Intra-articular (IA) injections of corticosteroids are used in equine practice for treatment of non-infectious synovitis and osteoarthritis. Trimacinolone acetonide (TACA) is a drug of choice. Pharmacokinetics (PK) of TACA administered IA to horses in the fetlock, carpal and antebrachiocarpal joint have been described. However, there are no PK reports on TACA 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.

Samples were collected prior to treatment and at 2-, 5- and 10-min post-administration with increasing intervals to 12 h. Plasma was analysed for the parent drug TACA only. Results were analysed by noncompartmental analysis using Phoenix WinNonLin software.

TACA was present in the blood 2 min after AI injection in 7 out of 10 horses and in all horses at 5 min post-injection. The Cmax was 1.6 ± 0.5 ng/mL at Tmax 5.9 ± 6.7 h. Elimination half-life was 28.2 ± 9.6 h with a mean residence time of 31.5 ± 9.9 h.

The drug was above the limit of quantification (LOQ = 0.03 ng/mL) in all horses up to 72 hours and remained above the limit of detection (LOD = 0.01 ng/mL) in five horses beyond 9 days. In one horse, plasma concentrations remained above the LOQ for the 9-day duration of the study.  The Australian Rules of Racing AR87 states that a horse subjected to an IA corticosteroid injection is ineligible to compete for 8-clear days. Therefore the 8-day clear rule would not be adequate for horses in this study.