Synovial and serum levels of triamcinolone following intra-articular administration of triamcinolone acetonide in the horse.

The research article explores the effects of intra-articular administration of triamcinolone in horses, indicating that the administered triamcinolone maintains presence in the synovial fluid for between 4 and 14 days while reaching the blood within an hour, affecting adrenal function for up to 4 days.

Research Methodology

• Seven mature thoroughbred horses, weighing between 400 and 541 kg, were used in the study. Each horse was injected intra-articularly in three joints with 6 mg/joint of triamcinolone. The fourth joint served as a control and was injected with saline.
• Synovial fluid from all four legs of the horses was collected on at intervals over 15 days post-injection. Similarly, blood was also collected over this timeframe.
• The collected synovial fluid and blood samples were analysed using radioimmunoassay to detect the levels of triamcinolone and cortisol.

Findings

• The research showed that one day after treatment, the triamcinolone level in the synovial fluid was 7.5 micrograms/milliliter, decreasing to 10 nanograms/milliliter by the fourth day. This reduced level was maintained for about a fortnight and was undetectable by the fifteenth day.
• In the blood, the concentration of triamcinolone increased to 3 ng/ml in the first hour, peaked at 4.3 ng/ml in the fourth hour, and fell to roughly 2 ng/ml in 24 hours. Within 48 hours, triamcinolone was nearly undetectable in the blood serum.
• Cortisol levels in the blood serum gradually decreased as the triamcinolone level increased. As the triamcinolone became undetectable on the second day, the cortisol concentrations gradually increased, returning to pre-administration levels by the fifth day.

Interpretations and Conclusions

• The study results indicate that intra-articular administration of triamcinolone maintains therapeutic concentrations in the synovial fluid for around 4-14 days.
• Triamcinolone entered the bloodstream within an hour of the intra-articular injection and remained detectable in the blood for about two days.
• An interesting finding noted was the inverse relationship between triamcinolone and cortisol in the blood serum, suggesting that triamcinolone inhibits adrenal function, which gradually recovers once the triamcinolone is metabolised and exits the body.