Pharmacokinetics of methocarbamol and phenylbutazone in exercised Thoroughbred horses

The medication violations in racehorses at Louisiana racetracks from 2016 to 2020

Introduction/Background

The number of publications for most common drug violations in racehorses is limited. This study reports the most common medication violations in racehorses at four major racetracks in Louisiana between 2016 and 2020.

Methods

During this 5‐year period, 27,237 blood samples and 25,672 urine samples collected during the course of normal race meeting activities were analysed by initial screening procedure utilizing Liquid Chromatography Mass Spectrometry (LC‐MS/MS). Following initial screening, suspect samples were subject to quantitative or semi‐ quantitative confirmation analysis by LC‐MS/MS.

Results

The total number of violations reported was 534 (1.01% of the total number of specimens analysed). The total number of violations reported in Thoroughbred horses was 210 while the total number of violations reported in Quarter Horses was 324. The percentage of total violations was %0.59 for all the specimens analysed in Thoroughbred horses while this percentage was %1.9 for all the specimens analysed in Quarter Horses during this 5‐year period. The most frequent violations included the overages (concentrations of permitted medications equal to or exceeding the set threshold) of clenbuterol (165 violations), non‐steroidal anti‐inflammatory drugs (NSAIDs) such as phenylbutazone (73 violations), combination of phenylbutazone with flunixin (45 violations) and muscle relaxant methocarbamol (40 violations).

Discussion/Conclusions

The total number of violations were relatively low during 5‐year period, but wide varieties of medications with different pharmacological actions were confirmed in performance horses in Louisiana. The most frequently reported violations in Louisiana were for permitted therapeutic medications (clenbuterol, phenylbutazone, flunixin methocarbamol) with established threshold and/or withdrawal guidelines in racehorses.

Multivariate optimization of a two-way technique for extraction of pharmaceuticals in surface water using a combination of membrane assisted solvent extraction and a molecularly imprinted polymer

This work demonstrates development and evaluation of a two-way technique based on the combination of membrane assisted solvent extraction and a molecularly imprinted polymer (MASE-MIP) for selective and efficient extraction of five selected pharmaceuticals belonging to five different therapeutic classes. The pharmaceuticals were extracted from surface water samples followed by liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-qTOF/MS) determination. A central composite design was applied to optimize the influence of the sample salt content, the stirring rate, the stirring time and the amount of MIP on the extraction of an anticonvulsant (carbamazepine), a cardiac stimulant (etilefrine), a muscle relaxant (methocarbamol), an antiretroviral (nevirapine) and an antidepressant (venlafaxine) from surface water. Optimization of the analytical method was performed by spiking water with a mixture of all five pharmaceuticals at 500 ng mL^-1. Optimum extraction conditions for a sample volume of 18 mL were found to be 5 g of salt content, a stirring rate of 400 rpm, an extraction time of 60 min and 50 mg of MIP. The MASE-MIP-LC-qTOF/MS method gave detection and quantification limits ranging from 0.09 to 0.20 ng mL^-1 and 0.31-0.69 ng mL^-1, respectively. The spiked river water samples yielded recoveries ranging from 38 to 91% for the selected model compounds belonging to the five classes of pharmaceuticals. Upon the application of the developed analytical method in water analysis, all selected pharmaceuticals were detected in South African river water with nevirapine and venlafaxine being more prominent attaining the maximum concentrations of 1.64 and 2.48 ng mL^-1, respectively.

Equine Cervical Pain and Dysfunction: Pathology, Diagnosis and Treatment

Simple Summary

Neck pain and dysfunction in the horse is becoming an increasingly important topic among riders, trainers and veterinarians. Some horses may present for a subtle performance decline, while others may show dramatic, dangerous behavior. It is important to recognize how to carefully evaluate the horse in an effort to understand the different types of pain that may be contributing to the different behaviors. The musculoskeletal and nervous systems may both play a role in the development of clinical signs. Recognizing that there are many diagnostic options as well as several treatments choices is important. This synopsis covers the disease processes that may contribute to the development of neck pain and dysfunction in the horse, as well as several possible diagnostic and treatment options.

Abstract

Interest in the cervical spine as a cause of pain or dysfunction is increasingly becoming the focus of many equine practitioners. Many affected horses are presented for poor performance, while others will present with dramatic, sometimes dangerous behavior. Understanding and distinguishing the different types of neck pain is a starting point to comprehending how the clinical presentations can vary so greatly. There are many steps needed to systematically evaluate the various tissues of the cervical spine to determine which components are contributing to cervical pain and dysfunction. Osseous structures, soft tissues and the central and the peripheral nervous system may all play a role in these various clinical presentations. After completing the clinical evaluation, several imaging modalities may be implemented to help determine the underlying pathologic processes. There are multiple treatment options available and each must be carefully chosen for an individual horse. Provided is a synopsis of the current knowledge as to different disease processes that can result in cervical pain and dysfunction, diagnostic approaches and treatment strategies. Improving the knowledge in these areas will ideally help to return horses to a state of well-being that can be maintained over time and through the rigors of their job or athletic endeavors.

Identification and characterization of the enzymes responsible for the metabolism of the non-steroidal anti-inflammatory drugs, flunixin meglumine and phenylbutazone, in horses

The in vivo metabolism and pharmacokinetics of flunixin meglumine and phenylbutazone have been extensively characterized; however, there are no published reports describing the in vitro metabolism, specifically the enzymes responsible for the biotransformation of these compounds in horses. Due to their widespread use and, therefore, increased potential for drug-drug interactions and widespread differences in drug disposition, this study aims to build on the limited current knowledge regarding P450-mediated metabolism in horses. Drugs were incubated with equine liver microsomes and a panel of recombinant equine P450s. Incubation of phenylbutazone in microsomes generated oxyphenbutazone and gamma-hydroxy phenylbutazone. Microsomal incubations with flunixin meglumine generated 5-OH flunixin, with a kinetic profile suggestive of substrate inhibition. In recombinant P450 assays, equine CYP3A97 was the only enzyme capable of generating oxyphenbutazone while several members of the equine CYP3A family and CYP1A1 were capable of catalyzing the biotransformation of flunixin to 5-OH flunixin. Flunixin meglumine metabolism by CYP1A1 and CYP3A93 showed a profile characteristic of biphasic kinetics, suggesting two substrate binding sites. The current study identifies specific enzymes responsible for the metabolism of two NSAIDs in horses and provides the basis for future study of drug-drug interactions and identification of reasons for varying pharmacokinetics between horses.

Pharmacokinetics and anti-inflammatory effects of flunixin meglumine as a sole agent and in combination with phenylbutazone in exercised Thoroughbred horses

BACKGROUND

Flunixin meglumine (FM) and phenylbutazone (PBZ) are potent anti-inflammatory agents and as such their potential to mask injuries that would otherwise keep a horse from training or racing is concerning. A common practice in racetrack medicine in the USA is to administer the two drugs within close proximity (24 hours apart) of each other, raising the concern of pharmacokinetic interactions and enhanced anti-inflammatory effects.

OBJECTIVES

Describe the pharmacokinetics and effects of PBZ on the clearance of FM when administered in close proximity as well as effects on inflammatory mediators.

STUDY DESIGN

Two-way randomised balanced crossover experiment.

METHODS

Twelve Thoroughbred exercised horses received 500 mg FM IV alone or in combination with 2 g of IV PBZ 24 hours later. Blood and urine samples were collected prior to and for up to 120 hours post-drug administration. Whole blood samples were collected at various times and challenged with lipopolysaccharide or calcium ionophore to induce ex vivo synthesis of eicosanoids. Concentrations of FM, PBZ and eicosanoids were measured using LC-MS/MS and noncompartmental pharmacokinetic analysis performed on concentration data.

RESULTS

Flunixin meglumine clearance was significantly increased when horses received PBZ 24 hours post-administration (P = .03). No other differences in pharmacokinetic parameters were noted between groups. Thromboxane B₂ was significantly suppressed, relative to baseline for 96 hours post-FM administration. Subsequent administration of PBZ prolonged the suppression. Prostaglandin E2 was decreased for 24 hours following administration of FM with subsequent administration of PBZ prolonging the suppression until 120 hours. PGF_2alpha concentrations were decreased for up to 168 hours post-FM administration. FM administration significantly decreased 15-HETE.

MAIN LIMITATIONS

Small sample size and lack of a phenylbutazone-only treatment group.

CONCLUSIONS

Administration of PBZ post-FM administration increased FM clearance. The anti-inflammatory effects of FM appear to be prolonged when PBZ is administered 24 hours post-administration.