Pharmacokinetics of furosemide in thoroughbred horses subjected to supramaximal treadmill exercise with and without controlled access to water.

BACKGROUND: The primary objective of this study was to assess the disposition of furosemide in Thoroughbred horses treated intravenously with 1 mg/kg of furosemide 4 and 24 h before supramaximal treadmill exercise without and with controlled access to water, respectively. Another objective was to determine whether furosemide was detectable in the plasma of horses after exposure to supramaximal treadmill exercise. Thoroughbred horses (n = 4-6) were administered single intravenous doses of 1 mg/kg of furosemide at 4 and 24 h before supramaximal exercise on a high-speed treadmill, with controlled and free access to water, respectively. Plasma furosemide concentrations were determined using liquid chromatography. RESULTS: Furosemide was detected in all the horses, regardless of whether they were treated 24 h or 4 h before excersice. In both treatment sequence groups of 2 horses, the concentration time profiles of furosemide during the first 4 h after its administration were relatively similar. The average maximum observed concentrations, AUC0-1.5h, and AUC0-3h, of both groups of horses were not different (p > 0.05). There were no significant differences in systemic clearance based on the geometric mean (95% confidence interval) (409 (347-482) mL/h/kg) for 4 h and 320 (177-580) mL/h/kg) for 24 h) between horses that were exercised 4- and 24-h post-furosemide administration. The plasma concentration of furosemide in all the horses fell below the limit of quantification (25 ng/mL) within 12 h after drug administration. In the group treated 24 h before exercise, none of the horses had detectable furosemide at the time of supramaximal treadmill exercise. In the group treated 4 h before exercise, furosemide was detected 1 h before and 2 h after supramaximal treadmill exercise in 4/4 and 3/4 horses, respectively. The mean AUC3-last h of both groups of horses were not different (p > 0.05). CONCLUSIONS: Water restriction did not exert any apparent effect on the disposition of furosemide. It remains to be determined, however, whether the attained plasma concentration of furosemide in combination with other controlled water access protocols have any direct or indirect pharmacological effect that may affect the athletic performance of the horse.

Plaintiff Attorney's Issues and Perspective: The Injured Worker as Claimant.

Injured workers deal with many struggles while healing, forced on them by problems within the workers' compensation system itself. The physician's role is critical in mitigating complicating factors that have a negative impact on recovery. The workers' compensation system is meant as a safety net, guaranteeing prompt medical care; therefore, the applicable causation standard is lower than scientific probability. Physicians treating injured workers must remember legal, ethical, and moral obligations to patients. Injured workers should not be treated differently from patients who suffered a similar injury at home. Nonmedical factors must be analyzed in deciding whether a person is legally disabled.

Pharmacokinetics and selected pharmacodynamics of cobalt following a single intravenous administration to horses.

Cobalt has been used by human athletes due to its purported performance-enhancing effects. It has been suggested that cobalt administration results in enhanced erythropoiesis, secondary to increased circulating erythropoietin (EPO) concentrations leading to improvements in athletic performance. Anecdotal reports of illicit administration of cobalt to horses for its suspected performance enhancing effects have led us to investigate the pharmacokinetics and pharmacodynamic effects of this compound when administered in horses, so as to better regulate its use. In the current study, 18 horses were administered a single intravenous dose of cobalt chloride or cobalt gluconate and serum and urine samples collected for up to 10 days post administration. Cobalt concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS) and pharmacokinetic parameters determined. Additional blood samples were collected for measurement of equine EPO concentrations as well as to assess any effects on red blood cell parameters. Horses were observed for adverse effects and heart rate monitored for the first 4 h post administration. Cobalt was characterized by a large volume of distribution (0.939 L/kg) and a prolonged gamma half-life (156.4 h). Cobalt serum concentrations were still above baseline values at 10 days post administration. A single administration of cobalt had no effect on EPO concentrations, red blood cell parameters or heart rate in any of the horses studied and no adverse effects were noted. Based on the prolonged gamma half-life and prolonged residence time, regulators should be able to detect administration of a single dose of cobalt to horses.

The pharmacokinetics of glycopyrrolate in Standardbred horses.

The disposition of plasma glycopyrrolate (GLY) is characterized by a three-compartment pharmacokinetic model after a 1-mg bolus intravenous dose to Standardbred horses. The median (range) plasma clearance (Clp), volume of distribution of the central compartment (V1 ), volume of distribution at steady-state (Vss), and area under the plasma concentration-time curve (AUC0-inf ) were 16.7 (13.6-21.7) mL/min/kg, 0.167 (0.103-0.215) L/kg, 3.69 (0.640-38.73) L/kg, and 2.58 (2.28-2.88) ng*h/mL, respectively. Renal clearance of GLY was characterized by a median (range) of 2.65 (1.92-3.59) mL/min/kg and represented approximately 11.3-24.7% of the total plasma clearance. As a result of these studies, we conclude that the majority of GLY is cleared through hepatic mechanisms because of the limited extent of renal clearance of GLY and absence of plasma esterase activity on GLY metabolism. Although the disposition of GLY after intravenous administration to Standardbred horses was similar to that in Thoroughbred horses, differences in some pharmacokinetic parameter estimates were evident. Such differences could be attributed to breed differences or study conditions. The research could provide valuable data to support regulatory guidelines for GLY in Standardbred horses.

The pharmacokinetics of methocarbamol and guaifenesin after single intravenous and multiple-dose oral administration of methocarbamol in the horse.

A simple LC/MSMS method has been developed and fully validated to determine concentrations and characterize the concentration vs. time course of methocarbamol (MCBL) and guaifenesin (GGE) in plasma after a single intravenous dose and multiple oral dose administrations of MCBL to conditioned Thoroughbred horses. The plasma concentration-time profiles for MCBL after a single intravenous dose of 15 mg/kg of MCBL were best described by a three-compartment model. Mean extrapolated peak (C0 ) plasma concentrations were 23.2 (± 5.93) µg/mL. Terminal half-life, volume of distribution at steady-state, mean residence time, and systemic clearance were characterized by a median (range) of 2.96 (2.46-4.71) h, 1.05 (0.943-1.21) L/kg, 1.98 (1.45-2.51) h, and 8.99 (6.68-10.8) mL/min/kg, respectively. Oral dose of MCBL was characterized by a median (range) terminal half-life, mean transit time, mean absorption time, and apparent oral clearance of 2.89 (2.21-4.88) h, 2.67 (1.80-2.87) h, 0.410 (0.350-0.770) h, and 16.5 (13.0-20) mL/min/kg. Bioavailability of orally administered MCBL was characterized by a median (range) of 54.4 (43.2-72.8)%. Guaifenesin plasma concentrations were below the limit of detection in all samples collected after the single intravenous dose of MCBL whereas they were detected for up to 24 h after the last dose of the multiple-dose oral regimen. This difference may be attributed to first-pass metabolism of MCBL to GGE after oral administration and may provide a means of differentiating the two routes of administration.

Pharmacokinetics and pharmacodynamics of glycopyrrolate following a continuous-rate infusion in the horse.

Glycopyrrolate (GLY) is an antimuscarinic agent that is used in humans and domestic animals primarily to reduce respiratory tract secretions during anesthesia and to reverse intra-operative bradycardia. Although GLY is used routinely in veterinary patients, there is limited information regarding its pharmacokinetic (PK) and pharmacodynamic (PD) properties in domestic animals, and an improved understanding of the plasma concentration-effect relationship in racehorses is warranted. To accomplish this, we characterize the pharmacokinetic-pharmacodynamic (PK-PD) actions of GLY during and after a 2-h constant-rate intravenous infusion (4 µg/kg/h) and evaluate potential PK-PD models for cardiac stimulation in adult horses. Measurements of plasma GLY concentrations, heart and respiration rates, and frequency of bowel movements were performed in six Thoroughbred horses. The time course for GLY disposition in plasma followed a tri-exponential equation characterized by rapid disappearance of GLY from blood followed by a prolonged terminal phase. Physiological monitoring revealed significant (P < 0.01) increases in heart (>70 bpm) and respiratory rates accompanied by a marked and sustained delay in the frequency of bowel movements (1.1 ± 0.2 h [saline group] vs. 6.0 ± 2.0 h [GLY group]). Two of six horses showed signs of colic during the 8-h observation period after the end of the GLY infusion, but were treated and recovered without further complications. The relationship between plasma GLY concentration and heart rate exhibited counterclockwise hysteresis that was adequately described using an effect compartment.

Comparison of PBTK model and biomarker based estimates of the internal dosimetry of acrylamide.

Estimates of internal dosimetry for acrylamide (AA, 2-propenamide; CASRN: 79-06-1) and its active metabolite glycidamide (GA) were compared using either biomarkers of internal exposure (hemoglobin adduct levels in rats and humans) or a PBTK model (Sweeney et al., 2010). The resulting impact on the human equivalent dose (HED, oral exposures), the human equivalent concentration (HEC, inhalation), and final reference values was also evaluated. Both approaches yielded similar AA HEDs and HECs for the most sensitive noncancer effect of neurotoxicity, identical oral reference doses (RfD) of 2×10(-3) mg AA/kg bw/d, and nearly identical inhalation reference concentrations (RfC=0.006 mg/m(3) and 0.007 mg/m(3), biomarker and PBTK results, respectively). HED and HEC values for carcinogenic potential were very similar, resulting in identical inhalation unit risks of 0.1/(mg AA/m(3)), and nearly identical oral cancer slope factors (0.4 and 0.5/mg AA/kg bw/d), biomarker and PBTK results, respectively. The concordance in estimated HEDs, HECs, and reference values from these two diverse methods increases confidence in those values. Advantages and specific application of each approach are discussed. (Note: Reference values derived with the PBPK model were part of this research, and do not replace values currently posted on IRIS: http://www.epa.gov/iris/toxreviews/0286tr.pdf.).

Pharmacokinetics and pharmacodynamics of tramadol in horses following oral administration.

Tramadol is a synthetic opioid used in human medicine, and to a lesser extent in veterinary medicine, for the treatment of both acute and chronic pain. In humans, the analgesic effects are owing to the actions of both the parent compound and an active metabolite (M1). The goal of the current study was to extend current knowledge of the pharmacokinetics of tramadol and M1 following oral administration of three doses of tramadol to horses. A total of nine healthy adult horses received a single oral administration of 3, 6, and 9 mg/kg of tramadol via nasogastric tube. Blood samples were collected at time 0 and at various times up to 96 h after drug administration. Urine samples were collected until 120 h after administration. Plasma and urine samples were analyzed using liquid chromatography-mass spectrometry, and the resulting data analyzed using noncompartmental analysis. For the 3, 6, and 9 mg/kg dose groups, Cmax , Tmax, and the t1/2λ were 43.1, 90.7, and 218 ng/mL, 0.750, 2.0, and 1.5 h and 2.14, 2.25, and 2.39 h, respectively. While tramadol and M1 plasma concentrations within the analgesic range for humans were attained in the 3 and 6 mg/kg dose group, these concentrations were at the lower end of the analgesic range and were only transiently maintained. Furthermore, until effective analgesic plasma concentrations have been established in horses, tramadol should be cautiously recommended for control of pain in horses. No significant undesirable behavioral or physiologic effects were noted at any of the doses administered.

A capillary absorption spectrometer for stable carbon isotope ratio (13C∕12C) analysis in very small samples.

A capillary absorption spectrometer (CAS) suitable for IR laser isotope analysis of small CO(2) samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO(2) near 2307 cm(-1) (4.34 µm). This initial CAS system can achieve relative isotopic precision of about 10 ppm (13)C, or ∼1 per thousand (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20-100 picomoles of entrained sample within the hollow waveguide for CO(2) concentrations ∼400-750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ∼2 Torr. Overall (13)C∕(12)C ratios can be calibrated to ∼2 per thousand accuracy with diluted CO(2) standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ∼10 s. The CAS is meant to work directly with converted CO(2) samples from a laser ablation-catalytic combustion micro-sampler to provide (13)C∕(12)C ratios of small biological isolates currently operating with spatial resolutions ∼50 µm.

Regulatory control of glycopyrrolate in performance horses using validated UHPLC/MS-MS methods.

We describe a validated, rapid, sensitive, and specific UHPLC-MS/MS method to detect and quantify glycopyrrolate in 0.5 mL of horse urine. Further, we investigated the elimination of glycopyrrolate in urine after both intravenous and oral administration of clinically relevant doses to Thoroughbred horses. Quantification was performed by weighted, linear regression analysis using a deuterated analogue of glycopyrrolate as internal standard (IS). The method was characterized by a linear range of 5-2500 pg/mL, a lower limit of quantification of 5 pg/mL and a limit of detection of 1 pg/mL. The intra and inter-batch imprecisions were <10% RSD and accuracy of the method ranged between 94 and 104%. Glycopyrrolate remained detectable in urine samples collected through 168 h after intravenous administration and through 24h after oral administration. Analytical method validation requirements for linearity, specificity, precision, accuracy, stability, dilution integrity, matrix effect, and ruggedness have been fulfilled. The urine method described in this report is simple and efficient and is the first reported method with sufficient sensitivity, accuracy, and precision to regulate the use of glycopyrrolate in urine samples collected more than one day after dosing of horses. Urine to plasma glycopyrrolate concentration ratios were calculated and were approximately 100:1 in samples collected from 24h through the end of sample collection.

Validation of a liquid chromatography-tandem mass spectrometry method for quantification of glycopyrrolate in horse plasma.

A rapid, sensitive, and specific ultra-high-performance liquid chromatography with heated electrospray ionization-tandem mass spectrometry (UHPLC-HESI-MS-MS) method to detect and quantify glycopyrrolate in horse plasma has been developed and validated. We also determined glycopyrrolate in plasma after oral and intravenous administration of clinically relevant doses to Thoroughbred horses. Calibration was accomplished by weighted, linear regression analysis using a deuterated analogue of glycopyrrolate as internal standard (IS). Glycopyrrolate (GLY) and the IS (GLY-d(3)) were isolated from plasma matrices via weak cation exchange using a simple solid-phase extraction technique. Chromatographic analysis was achieved by reversed-phase UHPLC on a C(18) Acquity™ column. Extracts were analyzed in positive electrospray ionization mode and precursor and product ions were detected and quantified by MS-MS using a triple-stage quadrupole (TSQ) instrument. The method was characterized by a linear range of 0.125-25 pg/mL (R(2) > 0.998), a lower limit of quantification of 0.125 pg/mL and a lower limit of detection of 0.025 pg/mL. Recovery of GLY ranged from 78% to 96%, and intra- and interbatch precision were 3.3-14.4%CV and 3.4-14.4%CV, respectively. Glycopyrrolate was stable in plasma for up to 170 days at -80°C, through three freeze/thaw cycles, and for up to 48 h after extraction under 20°C autosampler conditions.

An interlaboratory study of the pharmacokinetics of testosterone following intramuscular administration to Thoroughbred horses.

Testosterone is an anabolic androgenic steroid (AAS) that is endogenously produced by both male and female horses that also has the potential for abuse when administered exogenously to race horses. To recommend appropriate withdrawal guidelines so that veterinarians can discontinue therapeutic use prior to competition, the pharmacokinetics and elimination of testosterone were investigated. An aqueous testosterone suspension was administered intramuscularly in the neck of Thoroughbred horses (n = 20). The disposition of testosterone from this formulation was characterized by an initial, rapid absorption phase followed by a much more variable secondary absorption phase. The median terminal half-life was 39 h. A second focus of this study was to compare the testosterone concentrations determined by two different laboratories using a percentage similarity model with a coefficient of variation of 16.5% showing good agreement between the two laboratories results. Based on the results of this study, a withdrawal period of 30 days for aqueous testosterone administered IM is recommended.

Pharmacokinetics of detomidine administered to horses at rest and after maximal exercise.

REASON FOR PERFORMING STUDY: Increased doses of detomidine are required to produce sedation in horses after maximal exercise compared to calm or resting horses. OBJECTIVES: To determine if the pharmacokinetics of detomidine in Thoroughbred horses are different when the drug is given during recuperation from a brief period of maximal exercise compared to administration at rest. METHODS: Six Thoroughbred horses were preconditioned by exercising them on a treadmill. Each horse ran a simulated race at a treadmill speed that caused it to exercise at 120% of its maximal oxygen consumption. One minute after the end of exercise, horses were treated with detomidine. Each horse was treated with the same dose of detomidine on a second occasion a minimum of 14 days later while standing in a stocks. Samples of heparinised blood were obtained at various time points on both occasions. Plasma detomidine concentrations were determined by liquid chromatography-mass spectrometry. The plasma concentration vs. time data were analysed by nonlinear regression analysis. RESULTS: Median back-extrapolated time zero plasma concentration was significantly lower and median plasma half-life and median mean residence time were significantly longer when detomidine was administered after exercise compared to administration at rest. Median volume of distribution was significantly higher after exercise but median plasma clearance was not different between the 2 administrations. CONCLUSIONS AND POTENTIAL RELEVANCE: Detomidine i.v. is more widely distributed when administered to horses immediately after exercise compared to administration at rest resulting in lower peak plasma concentrations and a slower rate of elimination. The dose requirement to produce an equivalent effect may be higher in horses after exercise than in resting horses and less frequent subsequent doses may be required to produce a sustained effect.

Aminorex and rexamino as metabolites of levamisole in the horse.

Administration studies of levamisole in horses were carried out using two different levamisole preparations, namely, levamisole hydrochloride oral bolus and levamisole phosphate injectable solution. These preparations were analysed in detail for the presence of aminorex-like impurities. Both levamisole preparations were found to contain 1-(2-mercaptoethyl)-4-phenyl-2-imidazolidinone (I) and 4-phenyl-2-imidazolidinone (II) as degradation impurities, but neither aminorex nor rexamino was detected in these preparations. After the administration of these preparations to horses, aminorex, rexamino, in addition to levamisole and compound II, were detected in post-administration urine and plasma samples, among which compound II was found to have the longest detection time. Administration study of compound II was then performed on another horse to investigate whether it could be a metabolic precursor of aminorex and/or rexamino. However, no aminorex and rexamino was detected in the post-administration samples, suggesting that compound II was not a metabolic precursor of aminorex or rexamino. A metabolite (III) of compound II, tentatively identified to be a hydrolysis product of compound II, was observed instead. It has been established unequivocally that the normal use of levamisole products in horses can lead to the presence of aminorex, rexamino and 4-phenyl-2-imidazolidinone (II) in their urine and blood samples. As compound II has the longest detection time, the detection of aminorex (and in some cases rexamino) in some of the official samples from racehorses can be ascribed to the use of levamisole products as long as compound II is also present as a marker. These findings should be of direct relevance to the investigation of some of the cases of aminorex detection in official doping control samples from racehorses.

Pharmacokinetics of the calcium-channel blocker diltiazem after a single intravenous dose in horses.

The pharmacokinetics of diltiazem were determined in eight healthy horses. Diltiazem HCl, 1 mg/kg i.v., was administered over 5 min. Venous blood samples were collected at regular intervals after administration. Plasma concentrations of diltiazem and desacetyldiltiazem were determined by high-performance liquid chromatography. A second, putative metabolite was detected, but could not be identified due to the lack of an authentic standard. Data were analyzed by nonlinear least-squares regression analysis. The median (minimum-maximum) peak plasma concentration of diltiazem was 727 (539-976) ng/mL. Plasma diltiazem concentration vs. time data were best described by a two-compartment model with first-order drug elimination. The distribution half-life was 12 (6-23) min, the terminal half-life was 93 (73-161) min, the mean residence time was 125 (99-206) min, total plasma clearance was 14.4 (10.4-18.6) mL/kg/min, and the volume of distribution at steady-state was 1.84 (1.46-2.51) L/kg. The normalized ratio of the area under the curve (AUC) of desacetyldiltiazem to the AUC of diltiazem was 0.088 (0.062-0.179). The disposition of diltiazem in horses was characterized by rapid distribution and elimination and a terminal half-life shorter than reported in humans and dogs. Because of the reported low pharmacologic activity, plasma diltiazem metabolite concentrations were not considered clinically important.

Pharmacokinetic and pharmacodynamic evaluation of intravenous hydromorphone in cats.

This study describes the pharmacokinetics of intravenous hydromorphone in cats and the simultaneous measurement of antinociceptive pharmacodynamic effects using a thermal threshold testing system. Following establishment of a baseline thermal threshold, six adult cats were administered 0.1 mg/kg of hydromorphone intravenously. Thermal threshold testing and blood collection were conducted simultaneously at predetermined time points. Plasma hydromorphone concentrations were determined by a liquid chromatographic-mass spectral method and pharmacokinetic analysis was performed by nonlinear least squares regression analysis. Plasma hydromorphone concentrations declined rapidly over time, and were below the limit of quantification of the assay (LOQ = 1.0 ng/mL) by 360 min. In contrast, thermal thresholds rose from a pretreatment value of 40.9 +/- 0.65 degrees C (mean +/- SEM) to instrument cut-out (55 degrees C) within 15 min and remained significantly elevated from 15-450 min after treatment. Inspection of the data revealed no direct correlation between plasma hydromorphone concentrations and the antinociceptive effect of this drug in cats. These findings support the importance of conducting pharmacokinetic studies in parallel with objective measurements of drug effect.

DairyBeef: maximizing quality and profits--a consistent food safety message.

To respond to meat safety and quality issues in dairy market cattle, a collaborative project team for 7 western states was established to develop educational resources providing a consistent meat safety and quality message to dairy producers, farm advisors, and veterinarians. The team produced an educational website and CD-ROM course that included videos, narrated slide sets, and on-farm tools. The objectives of this course were: 1) to help producers and their advisors understand market cattle food safety and quality issues, 2) help maintain markets for these cows, and 3) help producers identify ways to improve the quality of dairy cattle going to slaughter. DairyBeef. Maximizing Quality & Profits consists of 6 sections, including 4 core segments. Successful completion of quizzes following each core segment is required for participants to receive a certificate of completion. A formative evaluation of the program revealed the necessity for minor content and technological changes with the web-based course. All evaluators considered the materials relevant to dairy producers. After editing, course availability was enabled in February, 2003. Between February and May, 2003, 21 individuals received certificates of completion.