Warfarin pharmacokinetics in the horse.

This research article investigates the pharmacokinetic properties of the drug warfarin in horses. Notably, it analyzes how the drug is absorbed, distributed, metabolized, and excreted in the body.

Study Participants and Methodology

• The study was conducted on 6 adult horses to understand the pharmacokinetics of racemic warfarin.
• Following intravenous administration, scientists monitored the plasma concentration of warfarin to observe its decline over time, which proved to be biphasic.
• Researchers analyzed the data as per the principles of 2-compartment kinetics (a pharmacokinetic model that considers a body to exist in two compartments – central and peripheral).

Key Findings

• Warfarin’s biological half-life in horses was measured to be 13.3 hours.
• The apparent volume of distribution was calculated to be 0.46 liters per kilogram (L X kg-1).
• The body clearance rate of warfarin came out to be 25.3 ml per hour per kilogram (ml X hour-1 X kg-1).
• A whopping 91.5% of warfarin was found to be bound to plasma proteins.
• Intriguingly, no unchanged warfarin was detected in the horses’ urine, suggesting its metabolic transformation.
• The absorption of warfarin from the gastrointestinal tract was observed to be nearly complete, underlining effective oral uptake.

Tissue Concentration of Warfarin

• The researchers also studied warfarin concentrations in different tissues of 4 foals who were administered warfarin orally and then euthanized after 14 hours.
• The concentration of warfarin in the kidneys was found to be twice that in plasma, reflecting selective distribution or perhaps reabsorption mechanisms.

Warfarin’s Effect on Blood Coagulation

• Examining the antithrombotic effect of warfarin, it was noted that this impact after both oral and intravenous administration (0.75 mg/kg of body weight) occurred only after 60 hours and lasted for about 30 hours.
• The effect of warfarin, though discernible, was relatively weak, with the maximum effect reflected in a 2.3-second elongation (from 11.5 seconds to 13.8 seconds) of thromboplastin time, a measure of the body’s clotting ability.