Pharmacokinetics of triamcinolone acetonide following intramuscular and intra-articular administration to exercised Thoroughbred horses.

This research investigates the plasma concentration and elimination rate of the drug triamcinolone acetonide (TA) in Thoroughbred racehorses after intramuscular and intra-articular administration. The findings emphasize the need for adequate withdrawal times before racing and highlight a discrepancy between drug concentrations in plasma, urine, and synovial fluid samples.

Research Methodology

• Twelve adult fit racing Thoroughbreds were given a single intramuscular (i.m.) dose of TA. Post the appropriate washout period, the same horses received a single intra-articular dose of TA.
• The researchers collected blood, urine, and synovial fluid samples before and at various points up to 60 days after administering the drug.
• The samples were analyzed using liquid chromatography-mass spectrometry and the plasma data was evaluated using noncompartmental analysis.

Results

• Results showed the peak plasma TA concentrations post 13.2 hours and 6.5 hours for intramuscular and intra-articular administration respectively.
• The plasma elimination half-life demonstrates the time body takes to reduce the drug’s concentration in plasma by half. The study found it to be approximately 11.4 days for i.m. administration and 0.78 days for intra-articular administration.
• Apart from plasma, the presence of the drug was also examined in urine and synovial fluid.
• Post i.m. administration, the drug was undetectable in plasma by Day 52 and in urine by Day 60. Post intra-articular administration, it was untraceable on Day 7 in plasma and Day 8 in urine.
• Interestingly, TA was undetectable in any sampled joints following i.m. administration but remained quantifiable till 21 days after intra-articular administration.

Conclusions

• This study adds to existing knowledge on how TA behaves in a horse’s body post administration via different routes.
• It pointed out the discrepencies between plasma, urine, and synovial fluid concentrations of TA, suggesting they may not be reliable indicators of each other.
• The study highlights the need for an extended withdrawal period for TA administered intramuscularly, as the drug remains detectable in the body for an extended period after administration.