Population pharmacokinetics of butorphanol following intramuscular administration to exercised thoroughbred horses.

Butorphanol is commonly administered, both by the intravenous and intramuscular routes, to racehorses to facilitate handling for diagnostic procedures. As the administration of butorphanol for therapeutic purposes is considered appropriate, in order to avoid inadvertent positive drug tests, a thorough understanding of the pharmacokinetics of this drug is necessary. In the current study, 12, exercised Thoroughbred horses were administered a single intramuscular dose of 0.1 mg/kg butorphanol, and serum and urine samples were collected at various times post drug administration for determination of butorphanol concentrations using a highly sensitive liquid chromatography tandem mass spectrometry method. Serum data were modeled using a nonlinear mixed effect population PK model. The maximum concentration (Cmax) and time to maximum concentration (Tmax) were 139.9 ± 72.8 ng/mL and 0.43 ± 0.44 h (mean ± SD), respectively. Although likely not clinically relevant, but important for drug testing purposes, a prolonged terminal phase was observed, yielding a terminal half-life of 7.67 ± 1.86 h. Using the blood screening limits proposed by the Horseracing Integrity and Welfare Unit, the detection time for intramuscular administration of butorphanol was estimated to be 96 h.

Pharmacokinetics and metabolism of lidocaine HCl 2% with epinephrine in horses following a palmar digital nerve block.

BACKGROUND: Lidocaine is a local anesthetic that is sometimes administered in combination with epinephrine. The addition of epinephrine increases the time lidocaine remains at the site of administration, thus prolonging the duration of effect. Due to their potential to prevent the visual detection of lameness, the administration of local anesthetics is strictly regulated in performance and racehorses. Recent reports of positive regulatory findings for lidocaine in racehorses suggests a better understanding of the behavior of this drug is warranted. The objective of the current study was to describe serum and urine concentrations and the pharmacokinetics of lidocaine and its primary metabolites following administration in combination with epinephrine, as a palmar digital nerve block in horses. Twelve horses received a single administration of 1 mL of 2% lidocaine HCl (20 mg/horse) with epinephrine 1:100,000, over the palmar digital nerve. Blood samples were collected up to 30 h and urine samples up to 48 h post administration. Lidocaine and metabolite concentrations were determined by liquid chromatography- mass spectrometry and pharmacokinetic (non-compartmental and compartmental) analysis was performed. RESULTS: Serum concentrations of lidocaine and 3-hydroxylidocaine were above the LOQ of the assay at 30 h post administration and monoethylglycinexylidide (MEGX) and glycinexylidide (GX) were below detectable levels by 24 and 48 h, respectively. In urine, lidocaine, MEGX and GX were all non-detectable by 48 h post administration while 3-hydroxylidocaine was above LOQ at 48 h post administration. The time of maximal concentration for lidocaine was 0.26 h (median) and the terminal half-life was 3.78 h (mean). The rate of absorption (Ka) was 1.92 1/h and the rate of elimination (Kel) was 2.21 1/h. CONCLUSIONS: Compared to previous reports, the terminal half-life and subsequent detection time observed following administration of lidocaine in combination with epinephrine is prolonged. This is likely due to a decrease in systemic uptake of lidocaine because of epinephrine induced vasoconstriction. Results of the current study suggest it is prudent to use an extended withdrawal time when administering local anesthetics in combination with epinephrine to performance horses.

Pharmacokinetics and effects of codeine in combination with acetaminophen on thermal nociception in horses.

Codeine and acetaminophen in combination have proven to be an effective analgesic treatment for moderate-to-severe and postoperative pain in humans. Studies have demonstrated that codeine and acetaminophen, when administered as sole agents, are well tolerated by horses. In the current study, we hypothesized that administration of the combination of codeine and acetaminophen would result in a significant thermal antinociceptive effect compared with administration of either alone. Six horses were administered oral doses of codeine (1.2 mg/kg), acetaminophen (20 mg/kg), and codeine plus acetaminophen (1.2 mg/kg codeine and 6-6.4 mg/kg acetaminophen) in a three-way balanced crossover design. Plasma samples were collected, concentrations of drug and metabolites determined via liquid chromatography-mass spectrometry, and pharmacokinetic analyses were performed. Pharmacodynamic outcomes, including effect on thermal thresholds, were assessed. Codeine Cmax and AUC were significantly different between the codeine and combination group. There was considerable inter-individual variation in the pharmacokinetic parameters for codeine, acetaminophen, and their metabolites in horses. All treatments were well tolerated with minimal significant adverse effects. An increase in the thermal threshold was noted at 1.5 and 2 h, from 15 min through 6 h and 0.5, 1, 1.5, and 3 h in the codeine, acetaminophen, and combination groups, respectively.

Concentrations, pharmacokinetics and selected pharmacodynamics of morphine and its active metabolites following oral administration to horses.

The metabolism and pharmacokinetics of intravenous (i.v.) morphine in the horse have been described; however, administration of therapeutic doses has also been associated with neuroexcitation and adverse gastrointestinal effects. In this study, we hypothesized that oral administration would lead to comparable concentrations of morphine and its presumed active metabolite, morphine 6-glucuronide (M6G) without the adverse effects associated with i.v. administration. Eight horses were administered a single i.v. dose of 0.2 mg/kg morphine and oral doses of 0.2, 0.6, and 0.8 mg/kg of morphine in a four-way balanced crossover design, with a 2-week washout period between doses. Concentrations of morphine and metabolites were determined, and pharmacokinetic parameters determined. Physiologic and behavioral outcomes including the number of steps taken, changes in heart rate, and gastrointestinal borborygmi were assessed. Oral administration of morphine resulted in higher concentrations of morphine metabolites, including M6G (Cmax : 11.6-37.8 ng/mL (0.6 mg/kg); 15.8-42.6 ng/mL (0.8 mg/kg)), compared with i.v. Bioavailability was 36.5%, 27.6% and 28.0% for 0.2, 0.6 and 0.8 mg/kg, respectively. Behavioral and physiologic changes were noted in all groups but were less prominent with oral compared with i.v. administration. Results of the current study are encouraging for further study, specifically anti-nociceptive effects of morphine following oral administration.

Pharmacokinetics and pharmacodynamics of intra-articular isoflupredone following administration to horses with lipopolysaccharide-induced synovitis.

BACKGROUND: Intra-articular corticosteroids, such as isoflupredone acetate, are commonly used in the treatment of joint inflammation, especially in performance horses. Following administration in a non-inflamed joints blood concentrations of isoflupredone were low and detectable for only a short period of time post-administration compared to synovial fluid concentrations. For some drugs, inflammation can affect pharmacokinetics, therefore, the goal of the current study was to describe the pharmacokinetics of isoflupredone acetate following intra-articular administration using a model of acute synovitis. Secondarily, pharmacodynamic effects, including effects on joint circumference, joint flexion, and lameness following intra-articular administration of isoflupredone acetate in the experimental model were described. METHODS: Sixteen horses received a single intra-articular dose of 8 mg of isoflupredone acetate or saline 12 h post-administration of lipopolysaccharide. Blood and urine samples were collected up to 72 h and synovial fluid for 28 days post-administration, drug concentrations determined by liquid chromatography- mass spectrometry and pharmacokinetic analysis performed. Joint circumference, maximum angle of pain free joint flexion and lameness were evaluated prior to and post-treatment. RESULTS: The maximum isoflupredone plasma concentration was 2.45 ± 0.61 ng/mL at 2.5 ± 0.75 h and concentrations were less than the limit of quantitation by 72 h. Isoflupredone was below detectable concentrations in urine by 72 h post-administration in all horses and no longer detectable in synovial fluid by 96 h post-administration. Joint circumference was significantly decreased in the isoflupredone treatment group compared to the saline group at 24 and 48 h post drug administration. Pain free joint flexion was significantly different between the saline and isoflupredone treatment groups on day 4 post-treatment. CONCLUSIONS: Synovial fluid concentrations and maximum plasma concentrations of isoflupredone differed slightly between the current study and a previous one describing administration into a non-inflamed joint, however, the detection time of isoflupredone in blood was comparable. Effects of isoflupredone on joint circumference and degree of pain free joint flexion suggest a short duration of effect with respect to alleviation of lipopolysaccharide induced synovitis, however, results of this study support future studies of the anti-inflammatory effects of intra-articular isoflupredone acetate.

Pharmacokinetics, adverse effects and effects on thermal nociception following administration of three doses of codeine to horses.

BACKGROUND: In humans, codeine is a commonly prescribed analgesic that produces its therapeutic effect largely through metabolism to morphine. In some species, analgesic effects of morphine have also been attributed to the morphine-6-glucuronide (M6G) metabolite. Although an effective analgesic, administration of morphine to horses produces dose-dependent neuroexcitation at therapeutic doses. Oral administration of codeine at a dose of 0.6 mg/kg has been shown to generate morphine and M6G concentrations comparable to that observed following administration of clinically effective doses of morphine, without the concomitant adverse effects observed with morphine administration. Based on these results, it was hypothesized that codeine administration would provide effective analgesia with decreased adverse excitatory effects compared to morphine. Seven horses received a single oral dose of saline or 0.3, 0.6 or 1.2 mg/kg codeine or 0.2 mg/kg morphine IV (positive control) in a randomized balanced 5-way cross-over design. Blood samples were collected up to 72 hours post administration, codeine, codeine 6-glucuronide, norcodeine morphine, morphine 3-glucuronide and M6G concentrations determined by liquid chromatography- mass spectrometry and pharmacokinetic analysis performed. Pre- and post-drug related behavior, locomotor activity, heart rate and gastrointestinal borborygmi were recorded. Response to noxious stimuli was evaluated by determining thermal threshold latency. RESULTS: Morphine concentrations were highest in the morphine dose group at all times post administration, however, M6G concentrations were significantly higher in all the codeine dose groups compared to the morphine group starting at 1 hour post drug administration and up to 72-hours in the 1.2 mg/kg group. With the exception of one horse that exhibited signs of colic following administration of 0.3 and 0.6 mg/kg, codeine administration was well tolerated. Morphine administration, led to signs of agitation, tremors and excitation. There was not a significant effect on thermal nociception in any of the dose groups studied. CONCLUSIONS: The current study describes the metabolic profile and pharmacokinetics of codeine in horses and provides information that can be utilized in the design of future studies to understand the anti-nociceptive and analgesic effects of opioids in this species with the goal of promoting judicious and safe use of this important class of drugs.

Pharmacokinetics of grapiprant and effects on TNF-alpha concentrations following oral administration to horses.

Grapiprant is a prostaglandin E2 receptor antagonist that has been found to be an effective anti-inflammatory in dogs and that is devoid of some of the adverse effects associated with traditional NSAIDs that elicit their effects through inhibition of PGE2 production. Previously published reports have described the pharmacokinetics of this drug in horses when administered at 2 mg/kg; however, pharmacodynamic effects in this species have yet to be described. The objective of the current study was to describe the pharmacokinetics and pharmacodynamics of grapiprant at a higher dose. Eight horses received a single oral administration of 15 mg/kg. Plasma concentrations were determined for 96 h using liquid chromatography-tandem mass spectrometry. Non-compartmental analysis was used to determine pharmacokinetic parameters. Pharmacodynamic effects were assessed ex vivo by stimulating blood samples with PGE2 and determining TNF-ɑ concentrations. Maximum concentration, time to maximum concentration and area under the curve were 327.5 (188.4-663.0) ng/ml, 1 (0.75-2.0) hour and 831.8 (512.6-1421.6) h*ng/ml, respectively. The terminal half-life was 11.1 (8.27-21.2) hr. Significant stimulation of TNF alpha was noted for 2-4 h post-drug administration. Results of this study suggest a short duration of EP4 receptor engagement when administered at a dose of 15 mg/kg.

Characterization of the pharmacokinetics, behavioral effects and effects on thermal nociception of morphine 6-glucuronide and morphine 3-glucuronide in horses.

OBJECTIVE: To describe the pharmacokinetics, behavioral and physiologic effects and effects on thermal thresholds of morphine, morphine 6-glucuronide (M6G) and morphine 3-glucuronide (M3G) following administration to horses. STUDY DESIGN: Randomized balanced crossover study. ANIMALS: A total of seven University-owned horses, five mares and two geldings, aged 3-6 years. METHODS: Horses were treated with a single intravenous dosage of saline, morphine (0.2 mg kg-1), M6G (0.01 mg kg-1) and M3G (0.03 mg kg-1). Blood was collected prior to (baseline) and at several times post administration. Drug and metabolite concentrations were determined by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were calculated. Behavioral observations and physiologic variables (heart rate, step counts, packed cell volume, total plasma protein and gastrointestinal sounds) were determined at baseline and for up to 6 hours. The effects on thermal nociception were determined and thermal excursion was calculated. RESULTS: The volumes of distribution were 4.75-10.5, 0.244-0.295 and 0.215-0.356 L kg-1 for morphine, M6G and M3G, respectively. Systemic clearances were 26.8-39.6, 3.16-3.88 and 1.46-2.13 mL minute-1 kg-1 for morphine, M6G and M3G, respectively. Morphine administration resulted in signs of excitation as evidenced by an increase in step counts and subjective behavioral observations, whereas M6G and M3G, based on the same criteria, appeared to cause sedative-like effects. Significant effects on thermal nociception were observed until 4 hours post morphine administration, 1 hour post M6G administration and at various times post M3G administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study provide additional information regarding the use of morphine in horses. Less locomotor excitation and gastrointestinal adverse effects, compared with morphine, coupled with favorable effects on thermal nociception are encouraging for further study of the pharmacodynamics of both M6G and M3G in horses.

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 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 Cmax , Tmax 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.

INTRAVENOUS IOPAMIDOL PHARMACOKINETICS IN COMMON CARP (CYPRINUS CARPIO).

Koi carp (Cyprinus carpio), a variety of common carp, has gained popularity as an ornamental fish worldwide. Their high monetary and sentimental value has necessitated the development of antemortem diagnostic options. Contrast-enhanced computed tomography (CT) scanning with intravenous iopamidol has been shown to be safe and diagnostically effective at a minimum dose of 480 mg iodine (I)/kg in koi. The purpose of this study was to evaluate the pharmacokinetic parameters of this dose of iopamidol, as well as excretory mechanisms specific to fish, using common carp as a model. Blood, posterior kidney, gill, and bile were collected, necessitating sacrificial sampling. Thirty-five adult fish were randomly divided into six sampling groups. Five sampling groups (n = 6/group) received 480 mg I/kg; the control group (n = 5) received an equivalent volume of saline. The iopamidol groups were sampled at the following time points postinjection: 5 min, 1 hr, 6 hr, 24 hr, and 48 hr. The control group was sampled at 48 hr. Concentrations of iopamidol were determined using liquid chromatography tandem mass spectrometry; noncompartmental analysis was used to calculate pharmacokinetic parameters. Total clearance (3.04 ml/hr per kilogram) was slower, the volume of distribution smaller (79.92 ml/ kg), and the elimination half-life (20.39 hr) prolonged compared to similar studies in mammals. The time-concentration profiles of kidney and gill were similar; these organs appear to be responsible for the majority of iopamidol excretion. However, that of bile was much different, showing slower, low-level accumulation with time, suggesting that in fish, multiple organ systems play a role in elimination beyond just the kidney. In particular, they may rely more heavily upon biliary excretion, which thus far has been noted only in mammals with renal impairment. Further research is warranted to investigate if the slower elimination allows diagnostic CT images to be acquired at different time points postinjection.

Meperidine pharmacokinetics and effects on physiologic parameters and thermal threshold following intravenous administration of three doses to horses.

BACKGROUND: Meperidine is a synthetic opioid that belongs to the phenylpiperidine class and is a weak mu receptor agonist. In horses there are a limited number of published studies describing the analgesic effects of systemically administered meperidine in horses. The objective of this study was to describe the pharmacokinetics, behavioral and physiologic effects and effect on thermal threshold of three doses of intravenously administered meperidine to horses. Eight University owned horses (four mares and four geldings, aged 3-8 years were studied using a randomized balanced 4-way cross-over design. Horses received a single intravenous dose of saline, 0.25, 0.5 and 1.0 mg/kg meperidine. Blood was collected before administration and at various time points until 96 hours post administration. Plasma and urine samples were analyzed for meperidine and normeperidine by liquid chromatography-mass spectrometry and plasma pharmacokinetics determined. Behavioral and physiologic data (continuous heart rate, step counts, packed cell volume, total plasma protein and gastrointestinal sounds) were collected at baseline through 6 hours post administration. The effect of meperidine administration on thermal nociception was determined and thermal excursion calculated. RESULTS: Meperidine was rapidly converted to the metabolite normeperidine. The volume of distribution at steady state and systemic clearance (mean ± SD) ranged from 0.829 ± 0.138-1.58 ± 0.280 L/kg and 18.0 ± 1.4-22.8 ± 3.60 mL/min/kg, respectively for 0.5-1.0 mg/kg doses. Adverse effects included increased dose-dependent central nervous excitation, heart rate and cutaneous reactions. Significant effects on thermal nociception were short lived (up to 45 minutes at 0.5 mg/kg and 15 minutes at 1.0 mg/kg). CONCLUSIONS: Results of the current study do not support routine clinical use of IV meperidine at a dose of 1 mg/kg to horses. Administration of 0.5 mg/kg may provide short-term analgesia, however, the associated inconsistent and/or short-term adverse effects suggest that its use as a sole agent at this dose, at best, must be cautiously considered.

Metabolism, pharmacokinetics and selected pharmacodynamic effects of codeine following a single oral administration to horses.

OBJECTIVE: To describe the pharmacokinetics and selected pharmacodynamic variables of codeine and its metabolites in Thoroughbred horses following a single oral administration. STUDY DESIGN: Prospective experimental study. ANIMALS: A total of 12 Thoroughbred horses, nine geldings and three mares, aged 4-8 years. METHODS: Horses were administered codeine (0.6 mg kg-1) orally and blood was collected before administration and at various times until 120 hours post administration. Plasma and urine samples were collected and analyzed for codeine and its metabolites by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were determined. Heart rate and rhythm, step counts, packed cell volume and total plasma protein were measured before and 4 hours after administration. RESULTS: Codeine was rapidly converted to the metabolites norcodeine, codeine-6-glucuronide (C6G), morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Plasma codeine concentrations were best represented using a two-compartment model. The Cmax, tmax and elimination t½ were 270.7 ± 136.0 ng mL-1, 0.438 ± 0.156 hours and 2.00 ± 0.534 hours, respectively. M3G was the main metabolite detected (Cmax 492.7 ± 35.5 ng mL-1), followed by C6G (Cmax 96.1 ± 33.8 ng mL-1) and M6G (Cmax 22.3 ± 4.96 ng mL-1). Morphine and norcodeine were the least abundant metabolites with Cmax of 3.17 ± 0.95 and 1.42 ± 0.79 ng mL-1, respectively. No significant adverse or excitatory effects were observed. CONCLUSIONS AND CLINICAL RELEVANCE: Following oral administration, codeine is rapidly metabolized to morphine, M3G, M6G, C6G and norcodeine in horses. Plasma concentrations of M6G, a presumed active metabolite of morphine, were comparable to concentrations reported previously following administration of an analgesic dose of morphine to horses. Codeine was well tolerated based on pharmacodynamic variables and behavioral observations.

Pharmacokinetics of hydroxyzine and cetirizine following oral administration of hydroxyzine to exercised Thoroughbred horses.

Hydroxyzine is a first-generation antihistamine and cetirizine, a second-generation antihistamine and active metabolite of hydroxyzine. Hydroxyzine is commonly used in performance horses and as such its use in closely regulated; however, there are no published studies suitable for establishing appropriate regulatory recommendations. In the current study, 12 exercised Thoroughbred research horses received a single oral administration of 500 mg of hydroxyzine. Blood and urine samples were collected prior to and up to 96 hr postdrug administration and concentrations of hydroxyzine and cetirizine determined using liquid chromatography-tandem mass spectrometry. A joint parent/metabolite population 2-compartment pharmacokinetic model with first-order absorption and elimination was utilized to describe the pharmacokinetics of both compounds. Serum hydroxyzine and cetirizine concentrations were above the limit of quantitation (0.1 ng/ml) of the assay at 96 hr (the last time point sampled). The terminal half-life was 7.41 and 7.13 hr for hydroxyzine and cetirizine, respectively. Findings from this study suggest that a prolonged withdrawal time should be observed if this compound is used in performance administered to performance horses and is classified as prohibited substance by the applicable regulatory body.

Pharmacokinetics and selected pharmacodynamics of morphine and its active metabolites in horses after intravenous administration of four doses.

The objective of the current study was to describe and characterize the pharmacokinetics and selected pharmacodynamic effects of morphine and its two major metabolites in horses following several doses of morphine. A total of ten horses were administered a single intravenous dose of morphine: 0.05, 0.1, 0.2, or 0.5 mg/kg, or saline control. Blood samples were collected up to 72 hr, analyzed for morphine, and metabolites by LC/MS/MS, and pharmacokinetic parameters were determined. Step count, heart rate and rhythm, gastrointestinal borborygmi, fecal output, packed cell volume, and total protein were also assessed. Morphine-3 glucuronide (M3G) was the predominant metabolite detected, with concentrations exceeding those of morphine-6 glucuronide (M6G) at all time points. Maximal concentrations of M3G and M6G ranged from 55.1 to 504 and 6.2 to 28.4 ng/ml, respectively, across dose groups. The initial assessment of morphine pharmacokinetics was done using noncompartmental analysis (NCA). The volume of distribution at steady-state and systemic clearance ranged from 9.40 to 16.9 L/kg and 23.3 to 32.4 ml min-1  kg-1 , respectively. Adverse effects included signs of decreased gastrointestinal motility and increased central nervous excitation. There was a correlation between increasing doses of morphine, increases in M3G concentrations, and adverse effects. Findings from this study support direct administration of purified M3G and M6G to horses to better characterize the pharmacokinetics of morphine and its metabolites and to assess pharmacodynamic activity of these metabolites.

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.

Pharmacokinetics of Ethyl Glucuronide and Ethyl Sulfate and Pharmacodynamic Effects Following Intravenous and Oral Administration of Ethanol to Exercised Horses.

Ethanol, a central nervous system depressant and banned substance in horseracing, has reportedly been administered to horses prior to competition to "calm a horse's nerves." In this study, the pharmacokinetics of two metabolites of ethanol were studied to better understand the behavior of this compound in the horse and provide a scientific basis for regulation of its administration. Six horses received a single intravenous (30 mL; 1200 mg) and oral (90 mL; 3600 mg) administration of ethanol (vodka, 40% ABV) in a balanced cross-over design. Blood and urine samples were collected at various times post administration for up to 24 h. Concentrations of ethyl glucuronide and ethyl sulfate were determined using liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis performed. Behavioral, locomotor activity and effects on heart rate were assessed. The maximum concentration (mean ± SD) of ethyl glucuronide was 71.5 ± 42.7 and 105.0 ± 47.5 ng/mL at 0.88 h following IV and oral administration, respectively. The maximum concentrations for the ethyl sulfate metabolite following IV and oral administration were 1.61 ± 0.60 and 3.46 ± 1.68 ng/mL, respectively. Urine concentrations of both metabolites were non-detectable by 24 h post ethyl alcohol administration. No observable behavioral responses were noted following IV or oral administration. Significant decreases in heart rate were noted at various times starting at 10 min until 4 h post administration in the oral dose group. Both ethyl glucuronide and ethyl sulfate could be useful markers for detection of illicit administration of ethanol to horses.

Pharmacokinetics and thermal anti-nociceptive effects of oral morphine in horses.

Introduction: Morphine is an effective analgesic in horses, however, IV administration at therapeutic doses has been shown to produce dose-dependent neuroexcitation and unwanted gastrointestinal effects. The analgesic effects of morphine have, at least in part, been attributed to the morphine-6-glucuronide (M6G) metabolite. Oral administration to horses results in comparable M6G concentrations to that achieved following IV administration of a therapeutic dose without the adverse effects. The anti-nociceptive effects have not yet been reported. In the current study the thermal anti-nociceptive effects of single and multiple oral doses of morphine were assessed. Methods: Six horses received a single 0.2 mg/kg IV dose of morphine and multiple oral doses of 0.8 mg/kg morphine every 12 h for 4.5 days. Blood samples were collected throughout administration, morphine, and metabolite concentrations determined and pharmacokinetic analysis performed. Drug related behavior and physiologic responses were recorded. Response to noxious stimuli was evaluated by determining thermal threshold latency in response to the application of heat. Results: The maximum concentrations of M6G were higher following oral administration compared to IV and the combined morphine and M6G concentrations exceeded that of IV administration starting at 2 h. Oral administration of 0.8 mg/kg morphine provided and maintained comparable anti-nociception effects to IV morphine with less adverse effects, following single and multiple doses. Morphine was well tolerated following oral administration with less excitation and minimal effects on gastrointestinal borborygmi scores compared to IV administration. Discussion: Results of the current study warrant further investigation of the anti-nociceptive effects of oral morphine administration to horses.

Clodronate detection and effects on markers of bone resorption are prolonged following a single administration to horses.

BACKGROUND: Clodronate is a potent antiresorptive agent labelled for use in horses over 4 years of age, for the treatment of navicular syndrome. Concerns regarding the extra-label use of clodronate in equine athletes, such as racehorses, have been raised as inhibition of osteoclast activity by clodronate has been postulated to interfere with normal bone healing, which is imperative to the repair of microfractures. The paucity of data describing the long-term pharmacokinetics of clodronate and effects on biomarkers of bone resorption necessitates further study. OBJECTIVES: (1) To determine clodronate concentrations in blood and urine over a 6-month period in horses undergoing treadmill exercise and (2) to assess the effects of clodronate on protein biomarkers of bone remodelling in this same group of horses. STUDY DESIGN: Randomised controlled experimental study. METHODS: Seven exercised Thoroughbred horses received a single im administration of 1.8 mg/kg clodronate and four horses received an equivalent volume of saline. Blood and urine samples were collected prior to, during and for 182 days post drug administration for drug concentration determination using liquid chromatography-tandem mass spectrometry, and determination of protein biomarker (CTX-1 and TRAcP5B) concentrations. RESULTS: Clodronate was detectable in blood for 14-175 days and for up to 175 days in urine. For some horses, concentrations were nondetectable at one time point but detectable at a subsequent time point. The terminal serum half-life ranged from 1.80 to 283.9 days. CTX-1 concentrations were significantly higher, relative to baseline, in both treated and control groups while concentrations of TRAcP5B were significantly lower in the treated group. MAIN LIMITATIONS: Relatively small number of horses studied. CONCLUSIONS: Based on assessment of protein biomarkers, clodronate appears to influence osteoclasts at label doses. Furthermore, results of this study support racing regulations that preclude horses administered bisphosphonates for medical reasons, from racing for a prolonged period of time.

CONTEXTO: Clodronato é um agente antirreabsortivo potente e recomendado para o uso em cavalos com mais de 4 anos de idade, para o tratamento da síndrome do navicular. Há preocupação com o uso indiscriminado de clodronato em equinos atletas, como cavalos de corrida, já que a inibição da atividade dos osteoclastos pelo clodronato tem sido postulada em interferir na cicatrização óssea normal, o que é essencial para a cicatrização de microfraturas. A escassez de informação quanto às ações prolongadas do uso de clodronato e seus efeitos nos biomarcadores de reabsorção óssea requere mais estudos. OBJETIVOS: (1) Determinar a concentração de clodronato no sangue e urina por um período de 6 meses em cavalos submetidos ao exercício em esteira e (2) acessar os efeitos de clodronato nos biomarcadores de remodelação óssea no mesmo grupo de cavalos. DELINEAMENTO DO ESTUDO: Estudo controlado randomizado. METODOLOGIA: Sete cavalos Puro-Sangue Inglês em exercício receberam uma única dose im de 1.8 mg/kg de clodronato e 4 cavalos receberam um volume equivalente de solução fisiológica. Amostras de sangue e urina foram coletadas antes, durante e por 182 dias após a administração de clodronato. Valores de concentração da droga foram determinados utilizando cromatografia líquida-espectrometria de massa (LC-MS/MS), e determinação da concentração de biomarcadores (CTX-1 e TRAcP5B) também foi realizada. RESULTADOS: Clodronato foi detectado no sangue por 14-175 dias e por até 175 dias na urina. Para alguns equinos, a concentração foi não-detectável em um momento, mas detectável no próximo momento. O valor terminal da vida-média em soro foi 1.80-283.9 dias. A concentração de CTX-1 foi significativamente elevada, relativo às amostras iniciais, em ambos os grupos (tratamento e controle), enquanto as concentrações de TRAcP5B foram significativamente menores no grupo de cavalos tratados. PRINCIPAIS LIMITAÇÕES: Número relativamente pequenos de cavalos no estudo. CONCLUSÕES: Baseado nos resultados dos biomarcadores, clodronato parece influencia osteoclastos na dose recomendada. Além disso, os resultados deste estudo suportam o regulamento de cavalos de corrida que impedem que cavalos que receberam bifosfonatos por razão médica de competir por um período de tempo prolongado.

Concentrations of dexmedetomidine and effect on biomarkers of cartilage toxicity following intra-articular administration in horses.

OBJECTIVE: The goal of this study was to determine plasma, urine, and synovial fluid concentrations and describe the effects on biomarkers of cartilage toxicity following intra-articular dexmedetomidine administration to horses. ANIMALS: 12 research horses. PROCEDURES: Horses received a single intra-articular administration of 1 µg/kg or 5 µg/kg dexmedetomidine or saline. Plasma, urine, and synovial fluid were collected prior to and up to 48 hours postadministration, and concentrations were determined. The effects on CS846 and C2C were determined in synovial fluid at 0, 12, and 24 hours postadministration using immunoassays. RESULTS: Plasma concentrations of dexmedetomidine fell below the limit of quantification (LOQ) (0.005 ng/mL) by 2.5 and 8 hours postadministration of 1 and 5 µg/kg, respectively. Synovial fluid concentrations were above the LOQ (0.1 ng/mL) of the assay at 24 hours in both dose groups. Drug was not detected in urine samples at any time postdrug administration. CS846 concentrations were significantly decreased relative to baseline at 12 hours postadministration in the saline group and significantly increased in the 5-µg/kg-dose group at 24 hours. Concentrations of C2C were significantly decreased at 12 and 24 hours postadministration in the saline treatment group. There were no significant differences in CS846 or C2C concentrations between dose groups at any time. CLINICAL RELEVANCE: Systemic concentrations of dexmedetomidine remained low, compared to synovial fluid concentrations. CS846, a marker of articular cartilage synthesis, increased in a dose-dependent fashion. Based on these findings, further dose titration and investigation of analgesic and adverse effects are warranted.