Phenylbutazone blood and urine concentrations, pharmacokinetics, and effects on biomarkers of inflammation in horses following intravenous and oral administration of clinical doses

Equine Veterinary Journal

Arthur

McKemie

et al. 2020

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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 B 2 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.

Section: Methodsmentioning

confidence: 99%

“…Eicosanoids concentrations in whole blood were determined using a previously described liquid chromatography‐tandem mass spectrometry method 9 …”

Section: Methodsmentioning

confidence: 99%

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

Equine Veterinary Journal

Arthur

McKemie

et al. 2020

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“…Liver microsomes were prepared as described previously (Knych, Arthur, et al, 2019; Knych, Baden, et al, 2019). Prior to performing microsomal incubations, linearity with respect to protein (enzyme activity) and time was established, and all subsequent kinetic studies were conducted within the linear portion of the rate curve.…”

Section: Methodsmentioning

confidence: 99%

“…Incubations were conducted to determine the specific P450 enzymes responsible for the biotransformation of FM and PBZ. Recombinant equine P450s (CYP1A1, 1A2, 3A89, 3A93, 3A94, 3A95, 3A96, 3A97, 2D14, 2D50, 2D82, and 2C92) and equine NADPH cytochrome P450 oxidoreductase enzymes were prepared and activity of all enzymes determined as described previously (Knych, Arthur, et al, 2019; Knych, Baden, et al, 2019).…”

Section: Methodsmentioning

confidence: 99%

“…This class of drugs is arguably the most commonly used medications in equine medicine, with phenylbutazone (PBZ) and flunixin meglumine (FM) being among the most frequently administered of the group. While the in vivo metabolism and pharmacokinetics of both drugs in horses have been extensively described (Gerring, Lees, & Taylor, 1981; Knych, Arthur, Mckemie, & Chapman, 2015; Knych, Arthur, et al, 2019; Knych, Baden, Gretler, & McKemie, 2019; Knych, Stanley, Seminoff, McKemie, & Kass, 2016; Lees, Landoni, Giraudel, & Touitain, 2004; Lees, Ewins, Taylor, & Sedgwick, 1987; Lees, Taylor, Maitho, Millar, & Higgins, 1987; Sams, Gerken, & Ashcraft, 1999; Semrad, Sams, Harris, & Ashcraft, 1993), to date, there are no published reports describing the in vitro metabolism of these compounds in horses. While these drugs undergo significant metabolism and only small amounts of parent compound are found in the urine, pharmacokinetic parameters reportedly vary greatly between individual animals (Knych et al., 2015, 2016; Knych, Arthur, et al, 2019; Knych, Baden, et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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

Vet Pharm & Therapeutics

Finno

Baden

et al. 2020

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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.

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

Drug Testing and Analysis

McKemie

Kass

et al. 2023

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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.