Pharmacokinetics of tilmicosin in equine tissues and plasma.

This research article investigates the pharmacokinetics, or how a drug is absorbed, distributed, metabolized, and eliminated by the body, of the antibiotic tilmicosin in horses. The researchers found that oral administration was ineffective, but subcutaneous administration showed higher tilmicosin levels in plasma and tissues, albeit with severe side effects at the injection site.

Methodology and Findings

• The research conducted was a pharmacokinetic study, aimed to evaluate how tilmicosin, a macrolide antibiotic, is processed by a horse’s body.
• Two methods of drug administration were tested: oral, at a dose of 4 mg/kg, and subcutaneous, at a dose of 10 mg/kg.
• The study found that no traces of tilmicosin were detected in equine plasma or tissues after oral administration.
• Subcutaneous administration demonstrated different results. Following subcutaneous injection, tilmicosin concentrations reached around 200 ng/mL in the horses’ plasma. Post-administration, plasma concentrations of tilmicosin persisted, with a mean residence time (MRT) – the average time the drug stays in the body – of 19 hours.
• Tilmicosin was also measured in different tissue types post-subcutaneous administration: in the lungs, kidneys, liver, and muscle of the horses. The Maximum tissue residue concentrations (Cmax) – the highest amount of the drug in the tissues – were 2784, 4877, 1398, and 881 ng/g respectively.
• The MRT of tilmicosin in these tissues was approximately 27 hours, longer than that noted in plasma.

Side Effects and Conclusions

• Despite its efficient absorption and distribution, subcutaneous administration of tilmicosin lead to severe reactions at the site of injection, indicating potential side effects of this form of administration.
• The conclusions drawn from the research indicate an ineffective absorption of tilmicosin when administered orally in horses, while subcutaneous administration demonstrated a more successful absorption and distribution process.
• However, the negative side effects observed at the site of subcutaneous injections suggest a need for further studies to determine the potential uses and optimizations of Tilmicosin administration in horses, particularly in regards to treating respiratory tract infections.