Pharmacokinetics of intravenous flumetasone and effects on plasma hydrocortisone concentrations and inflammatory mediators in the horse

Administration Studies in Equine Antidoping Research: Designing Scientific Investigations to Effectively Direct Medication Control in Racehorses

Pharmacokinetics is the study of the movement of drug in the body and includes the processes of absorption, distribution, metabolism, and excretion. Pharmacodynamics is the pharmacologic effect of the drug on the body. The pharmacokinetics of a drug determines its pharmacologic effect. Pharmacokinetic studies describe drug concentrations while pharmacodynamics allow for assessment of drug effects. Combined pharmacokinetic/pharmacodynamic studies allow for integration of drug concentrations with pharmacologic effect. Data generated from pharmacokinetic studies can be especially useful in establishing regulatory recommendations, determining appropriate thresholds, screening limits, administrative stand down times, and corresponding detection times. To generate the appropriate information, the following must be considered (1) the test subjects (i.e., number, age, breed, and fitness level), (2) selection of an appropriate dose/route and duration of administration, (3) sample matrix (blood, urine, and hair), (4) time(s) of sample collection, (5) development of an analytical method with appropriate sensitivity, and (6) what analytes to measure (parent and/or metabolite). Pharmacokinetic studies generate drug concentration data that can be used to calculate key pharmacokinetic variables necessary for establishing screening levels and detection times. Pharmacodynamic assessments can aid in understanding the pharmacologic effects of drugs and in correlating drug concentrations to these effects. Various models, including in vivo (whole animal), in vitro, and ex vivo assessments, can be utilized to determine pharmacodynamic effects. Factors to consider in the design of pharmacokinetic studies, basic pharmacokinetic parameters, and examples of pharmacodynamic assessments will be discussed in detail during this tutorial.

Analytical advances in horseracing medication and doping control from 2018 to 2023

The analytical approaches taken by laboratories to implement robust and efficient regulation of horseracing medication and doping control are complex and constantly evolving. Each laboratory's approach will be dictated by differences in regulatory, economic and scientific drivers specific to their local environment. However, in general, laboratories will all be undertaking developments and improvements to their screening strategies in order to meet new and emerging threats as well as provide improved service to their customers. In this paper, the published analytical advances in horseracing medication and doping control since the 22nd International Conference of Racing Analysts and Veterinarians will be reviewed. Due to the unprecedented impact of COVID-19 on the worldwide economy, the normal 2-year period of this review was extended to over 5 years. As such, there was considerable ground to cover, resulting in an increase in the number of relevant publications included from 107 to 307. Major trends in publications will be summarised and possible future directions highlighted. This will cover developments in the detection of 'small' and 'large' molecule drugs, sample preparation procedures and the use of alternative matrices, instrumental advances/applications, drug metabolism and pharmacokinetics, the detection and prevalence of 'endogenous' compounds and biomarker and OMICs approaches. Particular emphasis will be given to research into the potential threat of gene doping, which is a significant area of new and continued research for many laboratories. Furthermore, developments in analytical instrumentation relevant to equine medication and doping control will be discussed.

Ketoprofen in horses: Metabolism, pharmacokinetics, and effects on inflammatory biomarkers

Ketoprofen is an anti-inflammatory drug that is commonly administered to racehorses for the alleviation of musculoskeletal pain and inflammation. This study represents a comprehensive examination of the metabolism (in vivo and in vitro), pharmacokinetics and ex vivo pharmacodynamics, of ketoprofen in horses. The in vitro metabolism as well as specific enzymes responsible for metabolism was determined by incubating liver microsomes and recombinant CYP450 and UGT enzymes with ketoprofen. For the in vivo portion, 15 horses were administered a single intravenous dose of 2.2-mg/kg ketoprofen. Blood and urine samples were collected prior to and up to 120 h post-drug administration. Additional blood samples were collected at select time points and were stimulated with calcium ionophore or lipopolysaccharide, ex vivo, to induce eicosanoid production. Drug, metabolite, and eicosanoid concentrations were determined using LC-MS/MS. Incubation of ketoprofen with equine liver microsomes generated 3-hydroxy ketoprofen, an unidentified hydroxylated metabolite, and ketoprofen glucuronide. Recombinant equine CYP2C23 produced the greatest amount of hydroxylated ketoprofen and recombinant equine UGT1A2 generated ketoprofen glucuronide. Dihydro, 3-hydroxy, and glucuronide metabolites were identified in blood and urine samples. The Vdss was 0.280, 0.385, and 0.319 L/kg for total ketoprofen, S (+) ketoprofen, and R (-) ketoprofen, respectively. The mean half-life was 6.01 h for total ketoprofen, 2.22 h for S (+) ketoprofen, and 1.72 h for R (-) ketoprofen. Stimulation of ketoprofen-treated blood with lipopolysaccharide and calcium ionophore resulted in an inhibition of TXB2 , PGE2 , PGF2alpha , LTB4 , and 15(s)-HETE production for up to 120 h post-drug administration.

Changes in Heart Rate Variability with Induction of Gastric Ulcers in Adult Horses

Gastric ulceration can be induced by athletic training and is a significant welfare concern. The objective of this study was to evaluate the effect of gastric ulcer induction on heart rate variability (HRV) in the horse. We hypothesized that induction of gastric ulcers would decrease HRV and increase low frequency fluctuations, consistent with increased sympathetic tone. A convenience sample of 8 horses in a larger study were enrolled. Horses were randomly assigned to receive water or 2 mg/kg omeprazole orally once daily for 28 days. Gastric ulcers were induced through intermittent feed withholding on days 21 to 28. Gastroscopy was performed and gastric ulcers were graded (0-IV) by three blinded reviewers on days 21 and 28. Continuous electrocardiograms were obtained for one hour at the start and end of ulcer induction. HRV was assessed in 1-hour recordings for time domain variables and 5 minute sections for frequency domain analysis. HRV and ulcer grade across treatments were compared by a mixed effect model, with treatment and time as fixed effects and horse as a random effect. Gastric ulcer grade increased with induction protocol (P < .0001) and decreased with omeprazole treatment (P = .0007). Omeprazole treatment increased R-R intervals (P = .01) and decreased ratio of low frequency/high frequency signal (P = .008) as compared to horses receiving water. This was attributable to decreasing low frequency fluctuations (P = .05). While limited by the small sample size (four horses/treatment), this study suggests that omeprazole treatment decreases heart rate, and LF/HF ratio during ulcer induction, consistent with a decrease in sympathetic tone.

Towards Non-Targeted Screening of Lipid Biomarkers for Improved Equine Anti-Doping

The current approach to equine anti-doping is focused on the targeted detection of prohibited substances. However, as new substances are rapidly being developed, the need for complimentary methods for monitoring is crucial to ensure the integrity of the racing industry is upheld. Lipidomics is a growing field involved in the characterisation of lipids, their function and metabolism in a biological system. Different lipids have various biological effects throughout the equine system including platelet aggregation and inflammation. A certain class of lipids that are being reviewed are the eicosanoids (inflammatory markers). The use of eicosanoids as a complementary method for monitoring has become increasingly popular with various studies completed to highlight their potential. Studies including various corticosteroids, non-steroidal anti-inflammatories and cannabidiol have been reviewed to highlight the progress lipidomics has had in contributing to the equine anti-doping industry. This review has explored the techniques used to prepare and analyse samples for lipidomic investigations in addition to the statistical analysis and potential for lipidomics to be used for a longitudinal assessment in the equine anti-doping industry.

Measurements of Hydrocortisone and Cortisone for Longitudinal Profiling of Equine Plasma by LC-MS/MS

The conventional detection of exogenous drugs in equine doping samples has been used for confirmation and subsequent prosecution of participants responsible. In recent years, alternative methods using indirect detection have been investigated due to the expanding number of pharmaceutical agents available with the potential of misuse. The monitoring of endogenous biomarkers such as hydrocortisone (HC) has been studied in equine urine with an international threshold of 1 μg/ml established; however, there is no current threshold for equine plasma. The aim of this research was to investigate plasma concentrations of HC and cortisone (C) in race day samples compared to an administration of Triamcinolone Acetonide (TACA). The reference population (n = 1150) provided HC (6 to 145 ng/ml) and C (0.7 to 13 ng/ml) levels to derive the HC to C ratio (HC/C). Population reference limits (PRLs) were proposed for HC/C values at 0.2 (lower) and 61 (upper). Administration of TACA resulted in down‐regulation of HC/C values below the estimated PRLs for up to 96 h post‐administration. This indirect detection period was longer than the detection of TACA for 72 h. The use of individual reference limits (IRLs) for HC/C values was investigated to support the Equine Biological Passport (EBP), an intelligence model developed by Racing NSW for longitudinal monitoring of biomarkers.

Pharmacokinetics of transdermal flunixin meglumine and effects on biomarkers of inflammation in horses

Flunixin meglumine is a highly efficacious nonsteroidal anti-inflammatory drug commonly used in equine medicine and especially in performance horses. Recently, a new transdermal flunixin meglumine product has been approved for use in cattle. Although not currently approved for use in the horse, the convenience of this product may prove appealing for use in horses, warranting study. Six horses were administered a single transdermal dose of 500 mg and blood and urine samples collected for up to 96 h post-administration. Serum for determination of thromboxane concentrations and whole blood samples was collected at various time and challenged with lipopolysaccharide, calcium ionophore, or methanol to induce ex vivo synthesis of eicosanoids. Concentrations of flunixin, 5-OH flunixin, and eicosanoids were measured using LC-MS/MS and non-compartmental pharmacokinetic analysis performed on concentration data. Serum concentrations of flunixin and 5-OH flunixin were above the limit of quantitation at 96 h post-administration in both serum and urine. The mean (range) for C_max , T_max and the terminal half-life were 515.6 (369.7-714.0) ng/ml, 8.67 (8.0 12.0) h, and 22.4 (18.3-42.5) h, respectively. Following transdermal administration, based on effects on eicosanoid synthesis, flunixin meglumine inhibited cyclooxygenase 1 and 2 and 15-lipooxygenase activity, with anti-inflammatory effects lasting for 24-72 h.

Pharmacokinetics and effects on arachidonic acid metabolism of low doses of cannabidiol following oral administration to horses

The increasing availability of cannabidiol (CBD) and anecdotal reports of its anti-inflammatory effects has garnered it much interest in the equine industry. The objectives of the current study were to (1) describe the pharmacokinetics of oral CBD in exercising thoroughbreds, (2) characterize select behavioral and physiologic effects, and (3) evaluate effects on biomarkers of inflammation using an ex vivo model. This study was conducted in a randomized balanced 3-way crossover design with a two-week washout period between doses. Horses received a single oral dose (0.5, 1, and 2 mg/kg) of CBD suspended in sesame oil. Blood and urine samples were collected prior to and for 72 hr post drug administration. Additional blood samples collected at select time points were challenged ex vivo with calcium ionophore or lipopolysaccharide to induce eicosanoid production. Drug, metabolite, and eicosanoid concentrations were determined using LC-MS/MS. Cannabidiol was well tolerated with no significant behavioral, gastrointestinal, or cardiac abnormalities observed. CBD was readily absorbed, with parent drug detected in blood at all time points. The carboxylated and hydroxylated metabolites predominated in serum and urine, respectively. The terminal half-life for CBD was 10.7 ± 3.61, 10.6 ± 3.84 and 9.88 ± 3.53 for 0.5, 1, and 2 mg/kg. Although the effects were mixed, results of eicosanoid analysis suggest CBD affects COX-1, COX-2 and LOX at the doses studied here. Results of this study coupled with previous reports in other species, suggest further study of CBD in horses is warranted before its use as an anti-inflammatory can be recommended.

Serum concentrations, pharmacokinetic/pharmacodynamic modeling, and effects of dexamethasone on inflammatory mediators following intravenous and oral administration to exercised horses

Corticosteroids are potent anti-inflammatory drugs and as such are commonly administered to performance and racehorses. The objectives of the current study were to describe blood and urine concentrations and the pharmacokinetics and effects on cortisol and inflammatory mediator concentrations, following intravenous and oral administration to 12 exercised horses. Horses received an intravenous administration of 40 mg of dexamethasone sodium phosphate and 20 mg of dexamethasone tablets with a 4 week washout in between administrations. Blood and urine samples were collected prior to and for up to 96 hours post drug administration. Whole blood samples were collected at various time points and challenged with lipopolysaccharide or calcium ionophore to induce ex vivo synthesis of eicosanoids. The concentrations of dexamethasone and eicosanoids were measured using LC-MS/MS and the concentrations from both routes of administration fit simultaneously using a three-compartment pharmacokinetic model. A turnover model with inhibition of K_in gave an adequate fit to the dexamethasone-cortisol PKPD data. Serum and urine dexamethasone concentrations were at the limit of quantitation at 96 and 48 hours post administration, respectively. The volume of distribution, systemic clearance, and terminal half-life was 0.907 L/kg, 7.89 mL/h/kg, and 1.34 h, respectively. The IC₅₀ for cortisol suppression was 0.007 ng/mL. Stimulation of dexamethasone treated blood with lipopolysaccharide and calcium ionophore resulted in an inhibition of inflammatory biomarker production for a prolonged period of time post drug administration. The results of this study suggest that dexamethasone has a prolonged anti-inflammatory effect following intravenous or oral administration to horses.