Evaluation of plasma and urine pharmacokinetics of tranexamic acid for equine medication control

This study aimed to evaluate the pharmacokinetics (PK) of tranexamic acid (TXA) in horses and estimate its irrelevant plasma and urine concentrations using the pharmacokinetic/pharmacodynamic (PK/PD) approach by applying the Pierre-Louis Toutain model. TXA was intravenously administered to eight thoroughbred mares, and plasma and urine TXA concentrations were quantified by liquid chromatography/tandem mass spectrometry. The quantified data were used to calculate the PK parameters of TXA in horses. The plasma elimination curves were best-fitted to a three-compartment model. Using the Toutain model approach, irrelevant plasma and urine TXA concentrations were estimated to be 0.0206 and 0.997 μg/mL, respectively. The typical values of clearance, steady-state volume of distribution, and steady-state urine-to-plasma ratio were 0.080 L/kg/h, 0.86 L/kg, and 49.0, respectively. The obtained irrelevant concentrations will be useful for establishing relevant regulatory screening limits for effective control of TXA use in horse racing and equestrian sports.