Plasma and Urine Pharmacokinetics of Intravenous Pridinol in Thoroughbreds for Its Medication Control

We examined the pharmacokinetics of intravenous pridinol in six thoroughbred horses. Each horse received a single 20 mg dose of pridinol mesylate via the jugular vein, and plasma and urine samples were collected over 72 h. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to quantify pridinol concentrations in plasma and urine, allowing for the calculation of pharmacokinetic parameters. A three-compartment model best fit the plasma elimination data. Using the Toutain model, irrelevant plasma and urine concentrations were estimated to be 0.00284 and 0.000612 ng/mL, respectively. Key pharmacokinetic parameters were clearance rate, 1.27 L/h/kg; steady-state volume of distribution, 2.07 L/kg; and steady-state urine-to-plasma ratio, 0.211. These findings can help establish regulatory thresholds for pridinol in horse racing and equestrian sports.