Plasma and Urine Pharmacokinetics of Intravenous Pridinol in Thoroughbreds for Its Medication Control.
Abstract: 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.
© 2025 John Wiley & Sons Ltd.
Publication Date: 2025-10-09 PubMed ID: 41065090DOI: 10.1111/jvp.70029Google Scholar: Lookup
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- Journal Article
- Clinical Trial
- Veterinary
Summary
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Overview
- This study investigated how the drug pridinol behaves in the blood and urine of thoroughbred horses after being administered intravenously.
- The goal was to determine key pharmacokinetic parameters to help set medication control standards in horse racing and equestrian sports.
Purpose of the Study
- To examine the pharmacokinetics (absorption, distribution, metabolism, and excretion) of pridinol when given intravenously to thoroughbred horses.
- To provide scientific data that can be used in medication control by establishing relevant thresholds for pridinol detection in plasma and urine samples.
Methods
- Subjects: Six thoroughbred horses were used for the study.
- Dosage: Each horse received a single intravenous dose of 20 mg pridinol mesylate administered via the jugular vein.
- Sampling: Plasma and urine samples were collected over 72 hours following the drug administration.
- Analysis: Pridinol concentrations in plasma and urine were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS), a highly sensitive and specific technique.
- Pharmacokinetic Model: A three-compartment model was used to fit the elimination data from plasma samples.
- Threshold Estimation: The Toutain model was applied to estimate irrelevant plasma and urine concentrations, which indicate levels below which the drug is considered negligible.
Key Pharmacokinetic Findings
- Clearance Rate: 1.27 L/h/kg — indicating the volume of plasma from which pridinol is completely removed per hour per kilogram of horse’s body weight.
- Steady-State Volume of Distribution (Vss): 2.07 L/kg — reflecting the extent of drug distribution throughout body tissues relative to plasma.
- Steady-State Urine-to-Plasma Ratio: 0.211 — indicating the ratio of drug concentration in urine compared to plasma at steady state, useful for urine drug level interpretation.
- Three-Compartment Model: This suggests the drug distribution and elimination is complex, involving multiple body compartments describing initial distribution, slower tissue uptake, and elimination phases.
- Estimated Irrelevant Concentrations: Plasma concentration cutoff was 0.00284 ng/mL and urine concentration cutoff was 0.000612 ng/mL; below these the drug presence is considered insignificant for regulatory purposes.
Implications for Medication Control
- The pharmacokinetic data provide scientific basis to set regulatory thresholds or detection limits for pridinol in plasma and urine samples during doping control in horse racing and equestrian sports.
- The identified clearance rate, distribution volume, and urine-to-plasma ratio help to interpret the timing and extent of pridinol exposure.
- Establishing these thresholds ensures a fair competition by detecting illicit or excessive use of pridinol, which could affect horse performance or welfare.
Conclusion
- This study successfully characterized the plasma and urine pharmacokinetics of intravenous pridinol in thoroughbred horses.
- The results support the development of scientifically grounded medication control programs to monitor pridinol use in equine sports.
Cite This Article
APA
Minamijima Y, Kuroda T, Okano A, Wakuno A, Yuasa R, Ishikawa Y, Nomura M, Kinoshita K, Yamada M.
(2025).
Plasma and Urine Pharmacokinetics of Intravenous Pridinol in Thoroughbreds for Its Medication Control.
J Vet Pharmacol Ther, 49(1), 1-6.
https://doi.org/10.1111/jvp.70029 Publication
Researcher Affiliations
- Laboratory of Racing Chemistry, Tochigi, Japan.
- Equine Research Institute, Japan Racing Association, Tochigi, Japan.
- Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Japan Racing Association, Chiba, Japan.
- Equine Veterinary Clinic, Horse Racing School Anti-Doping Section, Equine Department, Japan Racing Association, Tokyo, Japan.
- Equine Veterinary Clinic, Horse Racing School Anti-Doping Section, Equine Department, Japan Racing Association, Tokyo, Japan.
- Equine Veterinary Clinic, Horse Racing School Anti-Doping Section, Equine Department, Japan Racing Association, Tokyo, Japan.
- Equine Veterinary Clinic, Horse Racing School Anti-Doping Section, Equine Department, Japan Racing Association, Tokyo, Japan.
- Equine Veterinary Clinic, Horse Racing School Anti-Doping Section, Equine Department, Japan Racing Association, Tokyo, Japan.
- Laboratory of Racing Chemistry, Tochigi, Japan.
- Laboratory of Racing Chemistry, Tochigi, Japan.
MeSH Terms
- Animals
- Area Under Curve
- Chromatography, Liquid / veterinary
- Doping in Sports
- Half-Life
- Horses / blood
- Horses / urine
- Horses / metabolism
- Injections, Intravenous / veterinary
- Muscle Relaxants, Central / blood
- Muscle Relaxants, Central / pharmacokinetics
- Muscle Relaxants, Central / urine
- Piperidines / blood
- Piperidines / pharmacokinetics
- Piperidines / urine
- Tandem Mass Spectrometry / veterinary
Grant Funding
- Laboratory of Racing Chemistry
- Japan Racing Association
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This article includes 16 references
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