Continuous measurement of caffeine and two metabolites in blood and skeletal muscle of unrestrained adult horses by semi-automated in vivo microdialysis.

The research studies the levels of caffeine and its two metabolites in the blood and muscles of adult horses using a semi-automatic microdialysis technique. It sheds light on the different pharmacokinetic behavior of caffeine and its metabolites in various tissues which can have implications for drug testing in large domesticated animals.

Objective and Methodology:

• The research aimed to measure the concentrations of caffeine, and its two metabolites, in the blood and muscle of adult horses.
• The study made use of a semi-automated in vivo microdialysis process to continuously sample from muscle tissues and the jugular vein for 48 hours.
• Levels of the substances were then determined using high-performance liquid chromatography (HPLC).

Findings:

• Following an intravenous injection of caffeine, a peak blood level averaging 5400 +/- 600 ng/mL was reached.
• The caffeine level then decreased with a half-life of roughly 15.3 +/- 0.7 hours.
• Contrary to expectations, noticeable pharmacokinetic differences were noticed between the muscle and blood samplings.
• The muscle tissues showed substantially higher concentrations of caffeine for 4 hours after drug administration.
• However, the measured levels of the caffeine metabolites, theophylline and theobromine, appeared delayed in both muscle and blood samples, reaching peak concentrations 1 day after caffeine administration.

Significance:

• The findings from the study highlight the dynamic and varied pharmacokinetic behavior of caffeine and its metabolites in different tissues within the body.
• The novel semi-automated microdialysis procedure used presents potential applications in continuous drug and metabolite level monitoring for large domesticated animals.