Warfarin pharmacokinetics in the horse

Area of Science:

• Veterinary Pharmacology
• Equine Pharmacokinetics

Background:

• Warfarin is an anticoagulant medication.
• Understanding its pharmacokinetics in horses is crucial for safe and effective use.

Purpose of the Study:

• To investigate the pharmacokinetics of racemic warfarin in adult horses.
• To evaluate tissue distribution and hypothrombogenic effects in horses.

Main Methods:

• Intravenous (IV) administration of warfarin to 6 adult horses.
• Plasma concentration analysis using a 2-compartment kinetic model.
• Tissue concentration analysis in 4 euthanatized foals.
• Assessment of hypothrombogenic effect after acute IV and oral administration.

Main Results:

• Warfarin exhibited a biphasic plasma decline with a biological half-life of 13.3 hours.
• High plasma protein binding (91.5%) and near-complete gastrointestinal absorption were observed.
• Kidney warfarin concentrations were approximately twice those in plasma.
• Hypothrombogenic effects were delayed (onset >60 hours), weak, and short-lived.

Conclusions:

• Warfarin demonstrates prolonged elimination and significant protein binding in horses.
• The anticoagulant effect in horses is weak and delayed, suggesting limited clinical utility for acute anticoagulation.
• Higher warfarin concentrations in kidney tissue warrant consideration.