Pharmacokinetics of methocarbamol and phenylbutazone in exercised Thoroughbred horses.
Abstract: Methocarbamol (MCBL) is commonly used in performance horses for the treatment of skeletal muscle disorders. Current regulatory recommendations for show horses and racehorses are based on a single oral dose of 5 g, although doses in excess of this are often administered. The goal of the current study was to characterize the disposition of MCBL following higher dose administration and administration in combination with another commonly used drug in performance horses, phenylbutazone (PBZ). Exercised Thoroughbred horses were administered various doses of MCBL as a sole agent and MCBL in combination with PBZ. Blood samples were collected at various times, concentrations of MCBL and PBZ measured using LC-MS/MS and pharmacokinetic parameters calculated using compartmental analysis. Following administration of 15 g of MCBL, either as part of a single- or multiple-dose regimen, a number of horses exceeded the Association of Racing Commissioners International and the United States Equestrian Federation's recommended regulatory threshold at the recommended withdrawal time. There was not a significant difference between horses that received only MCBL and those that received MCBL and PBZ. Results of the current study support an extended withdrawal guideline when doses in excess of 5 g are administered.
© 2016 John Wiley & Sons Ltd.
Publication Date: 2016-02-29 PubMed ID: 26924025DOI: 10.1111/jvp.12298Google Scholar: Lookup
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- Journal Article
Summary
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This research investigates the effects of administering methocarbamol (MCBL) and phenylbutazone (PBZ), both alone and in combination, to Thoroughbred horses who have been subjected to exercise. The study finds that current recommended withdrawal timelines for the drugs may be insufficient if higher-than-recommended doses are used.
Objective and Background
- The aim of the study was to understand the effect of administering MCBL, individually and in combination with PBZ, at higher doses than those currently recommended by the Association of Racing Commissioners International and the United States Equestrian Federation.
- The study was prompted due to common instances where these drugs were given in higher doses to performance horses for treating skeletal muscle disorders.
- MCBL and PBZ are commonly used drugs in racehorses and show horses.
Methodology of The Study
- Thoroughbred horses under exercise were administered varying doses of MCBL, either alone or in combination with PBZ.
- Blood samples were collected from these horses at different points in time to measure the concentration of MCBL and PBZ.
- The pharmacokinetic parameters were calculated using compartmental analysis.
Results and Finding of The Study
- It was found that several horses that were administered 15g of MCBL (three times higher than the recommended dose) exceeded the regulatory threshold recommended by racing and equestrian authorities at the recommended withdrawal time (the period before a race when a drug should be discontinued).
- The results remained consistent regardless of whether MCBL was administered as a single drug or in combination with PBZ.
- There was no significant difference observed between horses that received only MCBL and those that received both MCBL and PBZ.
Conclusion
- The study concluded that if horses received a dose higher than the recommended 5g of MCBL, an extended withdrawal period is suggested to maintain the drug concentration within accepted regulatory limits.
Cite This Article
APA
Knych HK, Stanley SD, Seminoff KN, McKemie DS, Kass PH.
(2016).
Pharmacokinetics of methocarbamol and phenylbutazone in exercised Thoroughbred horses.
J Vet Pharmacol Ther, 39(5), 469-477.
https://doi.org/10.1111/jvp.12298 Publication
Researcher Affiliations
- K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.
- Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA.
- K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.
- Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA.
- K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA.
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA.
MeSH Terms
- Administration, Oral
- Animals
- Anti-Inflammatory Agents, Non-Steroidal / administration & dosage
- Anti-Inflammatory Agents, Non-Steroidal / blood
- Anti-Inflammatory Agents, Non-Steroidal / pharmacokinetics
- Dose-Response Relationship, Drug
- Drug Interactions
- Drug Therapy, Combination
- Female
- Horses / blood
- Horses / metabolism
- Injections, Intravenous
- Male
- Methocarbamol / administration & dosage
- Methocarbamol / blood
- Methocarbamol / pharmacokinetics
- Muscle Relaxants, Central / administration & dosage
- Muscle Relaxants, Central / blood
- Muscle Relaxants, Central / pharmacokinetics
- Ointments / administration & dosage
- Phenylbutazone / administration & dosage
- Phenylbutazone / blood
- Phenylbutazone / pharmacokinetics
- Physical Conditioning, Animal
Citations
This article has been cited 3 times.- Waller P, Lomnicka I, Lucas C, Johnson S, Dirikolu L. The medication violations in racehorses at Louisiana racetracks from 2016 to 2020. Vet Med Sci 2022 Mar;8(2):553-560.
- Story MR, Haussler KK, Nout-Lomas YS, Aboellail TA, Kawcak CE, Barrett MF, Frisbie DD, McIlwraith CW. Equine Cervical Pain and Dysfunction: Pathology, Diagnosis and Treatment. Animals (Basel) 2021 Feb 6;11(2).
- Knych HK, Finno CJ, Baden R, Arthur RM, McKemie DS. Identification and characterization of the enzymes responsible for the metabolism of the non-steroidal anti-inflammatory drugs, flunixin meglumine and phenylbutazone, in horses. J Vet Pharmacol Ther 2021 Jan;44(1):36-46.
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