Dexamethasone serum concentrations after intravenous administration in horses during race training

Dexamethasone (DXM) sodium phosphate is a widely used corticosteroid for inflammatory conditions in horses, regulated in racing jurisdictions in the USA by a 0.005 ng/ml serum/plasma threshold. This study seeks to describe serum concentrations of DXM at 48 and 72 h after intravenous administration of 20 mg DXM sodium phosphate over 1 to 5 days, and to identify a possible source of DXM overages. 74 horses (39 Thoroughbreds, 13 Standardbreds, 22 Quarter Horses) in active race training received 20 mg DXM sodium phosphate. Serum was collected before injection, at 48 and 72 h post last injection, and analysed by LC/MS-MS (limit of quantification (LOQ) = 2.5 pg/ml). No differences were identified by ANOVA (P≤0.05) for racing breeds, age, gender or the number of days of DXM sodium phosphate administration, so data were pooled for each time point. The DXM serum concentration at 48 h (mean ± standard deviation, range) was 2.18±1.56 pg/ml (<2.5 to 40 pg/ml). Summary statistics could not be derived for 72 h DXM serum concentration data owing to censored data, but ranged from <2.5 to 95.8 pg/ml. There was one extreme outlier (Tukey) at 48 h, and two extreme outliers at 72 h. A separate study was conducted using sedentary experimental horses to determine the likelihood that positive DXM samples could result from environmental transfer. Urine was collected from a mare 2 to 3 h post administration of 20 mg DXM. Hay with 100 ml of the DXM (17 ng/ml) containing urine was offered to each of six experimental horses and blood was collected at 0, 4, 8, 12, 16, 20 and 24 h. All six horses had plasma DXM concentration above the limit of detection and five of six had plasma DXM concentrations above the LOQ for at least one sample time.

An interim screening limit of detection for naproxen in equine plasma: a review and analysis

Starting in August 2015 Thoroughbred racing in Charles Town, West Virginia experienced a sequence of intermittent low concentration Naproxen identifications from 6.3 to 161 ng/ml of plasma (27.3 to 699 nM). These identifications were ongoing, indicating the horsemen were unaware of their origins. Naproxen is administered orally to horses at substantial doses and is chemically stable in the environment. These identifications are therefore most likely associated with exposure of these horses to environmental traces of Naproxen. Given the low concentrations of these identifications, we were asked to identify a Screening Limit of Detection (SLOD) below which these trace level Naproxen identifications would not be reported. Review of the data set suggested an SLOD of 200 ng/ml, while outlier analysis suggested an ‘extreme’ outlier level at 247 ng/ml, which figure was rounded up to 250 ng/ml Naproxen or 1.09 uM. This proposed SLOD is in good agreement with other US regulatory thresholds for therapeutic medications and this Interim Screening Limit of Detection was presented for review.

Cobalt use and regulation in horseracing: a review

Cobalt, atomic weight 58.9, is a metallic element and environmental substance found in the animal in microgram quantities, predominantly as vitamin B12, but is also a component of at least one mammalian enzyme unassociated with B12. Cobalt is a required trace mineral and has long been administered as a dietary supplement to humans and animals. Cobalt deficiency outside of its requirement in vitamin B12 has not been reported in humans. The administration of cobalt salts was once standard treatment for anaemia in humans, owing to its ability to stimulate red blood cell synthesis. Elemental cobalt acts by stabilising hypoxia inducible factor (HIF-1α), which activates the erythropoietin gene, which in turn increases haemoglobin/red blood cell synthesis, which had led to a presumption that cobalt may be performance enhancing in athletes. Administration of cobalt in amounts sufficient to significantly increase the haematocrit are associated with risk of toxicity in humans, and the only cobalt administration study in horses showed no effect on red blood cell parameters or toxicity. Because of the perception that cobalt administration may enhance athletic performance, racing regulators have recently begun to restrict cobalt use in horseracing which has led to the introduction of cobalt thresholds in several racing jurisdictions. The International Federation of Horseracing Authorities is considering an international regulatory threshold for cobalt of 100 ng/ml in urine, based on studies performed in five different countries. In the United States, the Racing Commissioners International has recently set a primary plasma threshold of 25 ng/ml and secondary threshold of 50 ng/ml. One New York and New Jersey racetrack owner has initiated testing for cobalt and has denied his facilities to trainers whose horses tested positive for excessive quantities of cobalt. This review seeks to summarise what is known about the use of cobalt in horse racing.

Bovine colostrum supplementation optimises earnings, performance and recovery in racing Thoroughbreds

Bovine colostrum (BC) is the first milk produced by cows after calving and contains numerous beneficial substances for the immunity and development of the newborn calf. Because of the growth and immune factors in BC, it has become an attractive supplement for use by athletes to support immunity and health during athletic performance. In order to evaluate the effects of oral BC supplementation on equine athletes, this study evaluated the earnings, performance, recovery and incidence of upper respiratory infections (URTI) in racing horses. The study design was a randomized cross-over racing performance study. 21 horses in race training were randomly assigned to train and compete with or without BC supplementation. After each horse competed in three races, it was crossed over to the other group, allowed a three week washout period, and then competed in three additional races. Horses in public training stables of 3 participating trainers were used. Race performance as determined by earnings, Bloodstock Research Information System (BRIS) speed figures, recovery as determined by number of days between races and incidence of upper respiratory tract disease was recorded. 11 horses completed the study. There was no effect of the order of BC supplementation on the measured variables. Horses on BC supplementation earned $ 2,088 more purse money per race, than when unsupplemented (P=0.016), and ran an average of 5 BRIS speed points higher (P=0.03). Horses returned to racing on average 7.5 days faster (16.9 days vs 24.4 days, P=0.048). There were no URTI among the horses on BC supplementation and two infections while not on BC supplementation (z-test, P=0.11). Statistical analysis showed that horses recovered more quickly, earned three times more money and raced better as judged by BRIS scores while competing with BC supplementation. BC supplemented horses also experienced fewer URTI, although this effect was not significant.

Evaluation of mass spectrometric methods for detection of the anti-protozoal drug imidocarb

Imidocarb [N,N'-bis[3-(4,5-dihydro-1H-imidazol-2-yl)phenyl]urea, C(19)H(20)N(6)O(1), m.w. 348.41] is a symmetrical carbanilide derivative used to treat disease caused by protozoans of the Babesia genus. Imidocarb, however, is also considered capable of suppressing Babesia-specific immune responses, allowing Babesia-positive horses to pass a complement fixation test (CFT) without eliminating the infection. This scenario could enable Babesia-infected horses to pass CFT-based importation tests. It is imperative to unequivocally identify and quantify equine tissue residues of imidocarb by mass spectrometry to address this issue. As a pretext to development of sensitive tissue assays, we have investigated possibilities of mass spectrometric (MS) detection of imidocarb. Our analyses disclosed that an unequivocal mass spectral analysis of imidocarb is challenging because of its rapid fragmentation under standard gas chromatography (GC)-MS conditions. In contrast, solution chemistry of imidocarb is more stable but involves distribution into mono- and dicationic species, m/z 349 and 175, respectively, in acid owing to the compound's inherent symmetrical nature. Dicationic imidocarb was the preferred complex as viewed by either direct infusion-electrospray-MS or by liquid chromatography (LC)-MS. Dicationic imidocarb multiple reaction monitoring (MRM: m/z 175 → 162, 145, and 188) therefore offer the greatest opportunities for sensitive detection and LC-MS is more likely than GC-MS to yield a useful quantitative forensic analytical method for detecting imidocarb in horses.

Pemoline and tetramisole 'positives' in english racehorses following levamisole administration

Pemoline is a central nervous system stimulant that has been used to treat attention-deficit hyperactivity disorder and narcolepsy in humans; its identification in horses could be considered evidence of attempts to influence performance. Two recent pemoline 'positives' in English racehorses led us to review the chemical relationships between tetramisole, levamisole, aminorex and pemoline. Pemoline is a simple oxidation product of aminorex, which has been shown in the United States and elsewhere to be an equine metabolite of levamisole. Based on the clear structural relationships between aminorex and pemoline, we conclude that levamisole can metabolise to pemoline in horses and that pemoline identifications in horses post levamisole administration are likely to be associated with levamisole administration. Levamisole should not be administered to horses about to compete because of its ability to metabolise to two central nervous system stimulants, aminorex and pemoline.

Flexibility of an active center in sodium-plus-potassium adenosine triphosphatase

In plasma membranes of intact cells an enzymatic pump actively transports sodium ions inward and potassium ions outward. In preparations of broken membranes it appears as an adenosine triphosphatase dependent on magnesium, sodium, and potassium ions together. In this adenosine triphosphatase a phosphorylated intermediate is formed from adenosine triphosphate in the presence of sodium ions and is hydrolyzed with the addition of potassium ions. The normal intermediate was not split by adenosine diphosphate. However, selective poisoning by N-ethylmaleimide or partial inhibition by a low magnesium ion concentration yielded an intermediate split by adenosine diphosphate and insensitive to potassium ions. Pulse experiments on the native enzyme supported further a hypothesis of a sequence of phosphorylated forms, the first being made reversibly from adenosine triphosphate in the presence of sodium ion and the second being made irreversiblyfrom the first and hydrolyzed in the presence of potassium ion. The cardioactive steriod inhibitor, ouabain, appeared to combine preferentially with the second form. Phosphorylation was at the same active site according to electrophoretic patterns of proteolytic phosphorylated fragments of both reactive forms. It is concluded that there is a conformational change in the active center for phosphorylation during the normal reaction sequence. This change may be linked to one required theoretically for active translocation of ions across the cell membrane.

Trimetoquinol: bronchodilator effects in horses with heaves following aerosolised and oral administration

REASON FOR PERFORMING STUDY

The bronchodilator effects of trimetoquinol (TMQ) have been studied when administered i.v. or intratracheally, but not in an aerosolised form.

OBJECTIVES

To define the relationship between the therapeutic and adverse responses (therapeutic index) of TMQ when administered as an aerosol or by the oral route.

METHODS

Increasing doses of TMQ were administered to horses with heaves as an aerosol and by the oral route. Dose ranged 100-1000 microg/horse for aerosolised TMQ and from 6-60 microg/kg bwt for the oral route. Airway and cardiac effects were assessed by measurement of maximal change in pleural pressure (deltaPplmax) and heart rate (HR), respectively. Side effects of sweating, agitation and muscle trembling were scored subjectively. Duration of action of aerosolised (1000 pg/horse) and oral (6-60 microg/kg bwt) TMQ was evaluated over 6 h.

RESULTS

Aerosol administration of TMQ caused dose-dependent bronchodilation but did not change HR or cause other observable side effects. When 1000 microg/horse was administered via aerosol, TMQ produced a 2-phase bronchodilation; an immediate effect lasting up to 30 min and a second phase between 2 and 4 h. Oral TMQ was therapeutically ineffective.

CONCLUSION

Aerosol administration of TMQ is a safe and effective method of producing bronchodilation in horses.

Intravenous and intratracheal administration of trimetoquinol, a fast-acting short-lived bronchodilator in horses with ‘heaves’

REASON FOR PERFORMING STUDY

Trimetoquinol (TMQ) is a potent beta-adrenoceptor agonist bronchodilator used in human medicine but has not been evaluated for potential use as a therapeutic agent for horses with 'heaves'.

OBJECTIVES

To assess the pharmacodynamics of TMQ in horses with 'heaves' to determine potential therapeutic effects.

METHODS

Increasing doses of TMQ were administered to horses with 'heaves' by i.v. and intratracheal (i.t.) routes. Doses ranged 0.001-0.2 microg/kg bwt i.v. and 0.01-2 microg/kg bwt i.t. Cardiac and airways effects were assessed by measurement of heart rate (HR) and maximal change in pleural pressure (deltaPplmax), respectively. Side effects of sweating, agitation and muscle trembling were scored subjectively. Duration of action to i.v. (0.2 microg/kg bwt) and i.t. (2 microg/kg bwt) TMQ was evaluated over 6 h.

RESULTS

Intravenous TMQ was an exceptionally potent cardiac stimulant. Heart rate increased at 0.01 microg/kg bwt, and was still increasing after administration of highest dose, 0.2 microg/kg bwt. Airway bronchodilation, measured as a decrease in deltaPplmax, also commenced at 0.01 microg/kg bwt. By the i.t. route, TMQ was 50-100-fold less potent than by i.v. Side effects included sweating, agitation and muscle trembling. Overall, the onset of HR and bronchodilator effects was rapid, within about 3 min, but effects were over at 2 h.

CONCLUSION

When administered i.v. and i.t., TMQ is a highly potent cardiac stimulant and a modest bronchodilator. It may not be an appropriate pharmacological agent by i.v. and i.t. routes for the alleviation of signs in horses with 'heaves'. Further studies of TMQ by oral and aerosol routes are necessary.

POTENTIAL RELEVANCE

In horses, TMQ is a fast-acting bronchodilator with a short duration of action. It could be used as a rescue agent during an episode of 'heaves'. The i.v. and i.t. administration of TMQ is associated with side effects, similar to those reported for all other beta-agonists. However, other routes, such as aerosol and oral, may prove useful and safe for the alleviation of bronchoconstriction typical of 'heaves'.

Pyrilamine in the horse: detection and pharmacokinetics of pyrilamine and its major urinary metabolite O-desmethylpyrilamine

Pyrilamine is an antihistamine used in human and veterinary medicine. As antihistamines produce central nervous system effects in horses, pyrilamine has the potential to affect the performance of racehorses. In the present study, O-desmethylpyrilamine (O-DMP) was observed to be the predominant equine urinary metabolite of pyrilamine. After intravenous (i.v.) administration of pyrilamine (300 mg/horse), serum pyrilamine concentrations declined from about 280 ng/mL at 5 min postdose to about 2.5 ng/mL at 8 h postdose. After oral administration of pyrilamine (300 mg/horse), serum concentrations peaked at about 33 ng/mL at 30 min, falling to <2 ng/mL at 8 h postdose. Pyrilamine was not detected in serum samples at 24 h postdosing by either route. After i.v. injection of pyrilamine (300 mg/horse) O-DMP was recovered at a level of about 20 microg/mL at 2 h postdose thereafter declining to about 2 ng/mL at 168 h postdose. After oral administration, the O-DMP recovery peaked at about 12 microg/mL at 8 h postdose and declined to <2 ng/mL at 168 h postdose. These results show that pyrilamine is poorly bioavailable orally (18%), and can be detected by sensitive enzyme-linked immunosorbent assay tests in urine for up to 1 week after a single administration. Care should be taken as the data suggest that the withdrawal time for pyrilamine after repeated oral administrations is likely to be at least 1 week or longer.

ESI+ MS/MS confirmation of canine ivermectin toxicity

Ivermectin is a semisynthetic macrocyclic lactone anthelmintic of the avermectin family derived from Streptomyces fermentation products. Avermectins are used as antiparasitic agents in domestic animals; although considered relatively safe, one must consider animal species, breed, weight, and age in dosage determinations.In January 2006, two canines were presented to the UK Livestock Disease Diagnostic Center after dying from suspected ivermectin overdoses [30-50 mg/kg body weight]. To confirm this clinical diagnosis we developed a rapid, sensitive semiquantitative ElectroSpray Ionization-Mass Spectrometry (ESI/MS) method for ivermectin in canine tissue samples. Pharmaceutical ivermectin contains two ivermectins differing by a single methyl group, and each compound forms interpretation-confounding adducts with tissue Na(+) and K(+) ions. We now report that ivermectin administration was clearly confirmed by comparison with standard and dosage forms of ivermectin, and simple proportionalities based on mass spectral intensity of respective molecular ions allowed semiquantitative estimates of injection site tissue concentrations of 20 and 40 microg/g tissue (wet weight) in these animals, consistent with the history of ivermectin administration and the clinical signs observed.There is a distinct need for both rapid detection and confirmation of toxic exposures in veterinary diagnostics, whether for interpretation of clinical cases antemortem or for forensic reasons postmortem. It is vital that interpreters of analytical results have appropriate guidance in the scientific literature and elsewhere so as to enable clear-cut answers. The method presented here is suitable for routine diagnostic work in that it allows rapid extraction of ivermectin from tissue samples, avoids the need for high-performance liquid chromatography and allows ready interpretation of the multiple ivermectin species seen by ESI(+) MS/MS in samples originating from veterinary dosage forms.

Plasma and urinary concentrations of trimetoquinol by LC-MS-MS following intravenous and intra-tracheal administration to horses with heaves

Trimetoquinol (TMQ) is a very potent and fast acting bronchodilator in horses with heaves. This study assessed the plasma and urinary concentrations of TMQ in horses with heaves following administration via the intravenous (IV, 0.2 microg/kg) and intra-tracheal (IT, 2 microg/kg) routes. TMQ was administered to six horses affected with heaves (RAO - Recurrent Airway Obstruction, used interchangeably) by the above routes and plasma and urine samples collected and stored at -20 degrees C until analyzed. Solid Phase Extraction (SPE) of TMQ was followed by highly sensitive ESI(+)-LC-MS-MS (ElectroSpray Ionization, positive mode - Liquid Chromatography - Mass Spectrometry - Mass Spectrometry); with a Limit of Detection (LOD) estimated at 1 pg/mL. Following IV administration, TMQ plasma levels peaked at 1 min at 707 pg/mL, and at 9 min at 306 pg/mL following IT administration. Our results show that TMQ plasma concentrations decline rapidly following IV administration, which is consistent with the fast onset and short duration of TMQ effect that was observed in our previous studies. On the other hand, IT administration showed a very unique plasma concentration pattern. From a regulatory standpoint, the current available TMQ ELISA kit was also used in an attempt to detect TMQ from the plasma and urine samples. We report that the ELISA kit was unable to detect TMQ from any of the samples generated in these studies.

Development of a method for the detection and confirmation of the alpha-2 agonist amitraz and its major metabolite in horse urine

Amitraz (N'-(2,4-dimethylphenyl)-N-[[(2,4-dimethylphenyl)imino]methyl]-N-methyl-methanimidamide) is an alpha-2 adrenergic agonist used in veterinary medicine primarily as a scabicide- or acaricide-type insecticide. As an alpha-2 adrenergic agonist, it also has sedative/tranquilizing properties and is, therefore, listed as an Association of Racing Commissioners International Class 3 Foreign Substance, indicating its potential to influence the outcome of horse races. We identified the principal equine metabolite of amitraz as N-2,4-dimethylphenyl-N'-methylformamidine by electrospray ionization(+)-mass spectrometry and developed a gas chromatographic-mass spectrometric (GC-MS) method for its detection, quantitation, and confirmation in performance horse regulation. The GC-MS method involves derivatization with t-butyldimethylsilyl groups; selected ion monitoring (SIM) of m/z 205 (quantifier ion), 278, 261, and 219 (qualifier ions); and elaboration of a calibration curve based on ion area ratios involving simultaneous SIM acquisition of an internal standard m/z 208 quantifier ion based on an in-house synthesized d(6) deuterated metabolite. The limit of detection of the method is approximately 5 ng/mL in urine and is sufficiently sensitive to detect the peak urinary metabolite at 1 h post dose, following administration of amitraz at a 75-mg/horse intravenous dose.

Detection and Confirmation of Ractopamine and Its Metabolites in Horse Urine After Paylean® Administration*

We have investigated the detection, confirmation, and metabolism of the beta-adrenergic agonist ractopamine administered as Paylean to the horse. A Testing Components Corporation enzyme-linked imunosorbent assay (ELISA) kit for ractopamine displayed linear response between 1.0 and 100 ng/mL with an I-50 of 10 ng/mL and an effective screening limit of detection of 50 ng/mL. The kit was readily able to detect ractopamine equivalents in unhydrolyzed urine up to 24 h following a 300-mg oral dose. Gas chromatography-mass spectrometry (GC-MS) confirmation comprised glucuronidase treatment, solid-phase extraction, and trimethylsilyl derivatization, with selected-ion monitoring of ractopamine-tris(trimethylsilane) (TMS) m/z 267, 250, 179, and 502 ions. Quantitation was elaborated in comparison to a 445 Mw isoxsuprine-bis(TMS) internal standard monitored simultaneously. The instrumental limit of detection, defined as that number of ng on column for which signal-to-noise ratios for one or more diagnostic ions fell below a value of three, was 0.1 ng, corresponding to roughly 5 ng/mL in matrix. Based on the quantitation ions for ractopamine standards extracted from urine, standard curves showed a linear response for ractopamine concentrations between 10 and 100 ng/mL with a correlation coefficient r > 0.99, whereas standards in the concentration range of 10-1000 ng/mL were fit to a second-order regression curve with r > 0.99. The lower limit of detection for ractopamine in urine, defined as the lowest concentration at which the identity of ractopamine could be confirmed by comparison of diagnostic MS ion ratios, ranged between 25 and 50 ng/mL. Urine concentration of parent ractopamine 24 h post-dose was measured at 360 ng/mL by GC-MS after oral administration of 300 mg. Urinary metabolites were identified by electrospray ionization (+) tandem quadrupole mass spectrometry and were shown to include glucuronide, methyl, and mixed methyl-glucuronide conjugates. We also considered the possibility that an unusual conjugate added 113 amu to give an observed m/z 415 [M+H] species or two times 113 amu to give an m/z 528 [M+H] species with a daughter ion mass spectrum related to the previous one. Sulfate and mixed methyl-sulfate conjugates were revealed following glucuronidase treatment, suggesting that sulfation occurs in combination with glucuronidation. We noted a paired chromatographic peak phenomenon of apparent ractopamine metabolites appearing as doublets of equivalent intensity with nearly identical mass spectra on GC-MS and concluded that this phenomenon is consistent with Paylean being a mixture of RR, RS, SR, and SS diastereomers of ractopamine. The results suggest that ELISA-based screening followed by glucuronide hydrolysis, parent drug recovery, and TMS derivatization provide an effective pathway for detection and GC-MS confirmation of ractopamine in equine urine.

A GC-MS Method for the Determination of Isoxsuprine in Biological Fluids of the Horse Utilizing Electron Impact Ionization*

Isoxsuprine is used to treat navicular disease and other lower-limb problems in the horse. Isoxsuprine is regulated as a class 4 compound by the Association of Racing Commissioners, International (ARCI) and, thus, requires regulatory monitoring. A gas chromatography-mass spectrometry method utilizing electron impact ionization was developed and validated for the quantitation of isoxsuprine in equine plasma or equine urine. The method utilized robotic solid-phase extraction and tri-methyl silyl ether products of derivatization. Products were bis-trimethylsilyl (TMS) isoxsuprine and tris-TMS ritodrine, which released intense quantifier ions m/z 178 for isoxsuprine and m/z 236 for ritodrine that were products of C-C cleavage. To our knowledge, this procedure is faster and more sensitive than other methods in the literature. Concentrations in urine and plasma of isoxsuprine were determined from a calibrator curve that was generated along with unknowns. Ritodrine was used as an internal standard and was, therefore, present in all samples, standards, and blanks. Validation data was also collected. The limit of detection of isoxsuprine in plasma was determined to be 2 ng/mL, the limit of quantitation of isoxsuprine in plasma was determined to be < 5 ng/mL. The mean coefficient of determination for the calibrator curves for plasma was 0.9925 +/- 0.0052 and for calibrator curves for urine 0.9904 +/- 0.0075. The recovery efficiencies at concentrations of 50, 200, and 300 ng/mL were 76%, 73%, and 76%, respectively, in plasma and 92%, 89%, and 91% in urine.

Toxicological evaluation of long-term intravenous administration of amitraz in horses

With the aim of determining the possible toxicity of amitraz after its prolonged use in horses, six English Thoroughbred horses received intravenous injections of amitraz (0.05, 0.10 or 0.15 mg/kg) weekly for four months, constituting the experimental group. Eight other animals (control group), via the same route following the same drug administration schedule and period of time, received the vehicle, dimethylformamide. At the end of this period, blood was collected from all the animals, and a comparison was made of the means of the values obtained for the various blood analyses: complete hemogram, alkaline phosphatase, gamma-glutamyltransferase, blood urea nitrogen, lactate dehydrogenase, aspartate aminotransferase, creatine phosphokinase, glucose, albumin, total protein, creatinine, Na+ , K+, Cl- and CO2. The results for the biochemical characteristics showed that only the mean value for urea of the animals submitted to treatment with amitraz was significantly different than the mean value obtained for the control group. The analyses of the hematological characteristics showed that no significant differences between groups were observed. Similarly, the measurement of blood electrolyte levels demonstrated that long-term treatment with amitraz did not cause significant changes in the variables analyzed. The results indicate that amitraz, given in the doses employed in this study, did not show signs of inducing toxic effects in vital organs, even after prolonged administration.

Determination of the highest no-effect dose (HNED) and of the elimination pattern for cocaine in horses

Cocaine is one of the most widespread illegal stimulants utilized by the human population throughout the world. The aim of this study was to establish the highest no-effect dose (HNED) of cocaine on the spontaneous locomotor activity (SLA) of horses in a behavior chamber, and thereby to determine the maximal acceptable threshold of the urinary drug concentration in horses. Twelve English thoroughbred mares received 0.02, 0.03, 0.04, 0.08 or 0.12 mg kg(-1) cocaine i.v. or saline solution (control). It was noted that doses above 0.04 mg kg(-1) induced a significant increase in SLA (P < 0.05, Tukey's test). No significant increase in SLA was seen in the mares that received 0.03 mg kg(-1), but the animals showed important behavioral changes that did not occur after the 0.02 mg kg(-1) dose. It was concluded that the HNED of cocaine for horses in a behavior chamber is 0.02 mg kg(-1). After injection of this dose in five horses, urine samples were collected at predetermined intervals through vesical catheterization. The concentrations of cocaine, norcocaine, benzoylecgonine and ecgonine methyl ester were quantified by liquid chromatography/electrospray ionization tandem mass spectrometry. Cocaine and norcocaine concentrations remained consistently below the level of detection. Benzoylecgonine reached a mean (+/- SEM) maximum concentration of 531.9 +/- 168.7 ng ml(-1) after 4 h, whereas ecgonine methyl ester peaked 2 h after injection at a concentration of 97.2 +/- 26.5 ng ml(-1). The maximum admissible concentration for cocaine and/or metabolites in the urine of horses is difficult to establish unequivocally because of the substantial individual variation in the drug elimination pattern observed in horses, which can be inferred by the large standard error of the means obtained.

Comparison of the quantification of caffeine in human plasma by gas chromatography and ELISA

In the present study we evaluated the precision of the ELISA method to quantify caffeine in human plasma and compared the results with those obtained by gas chromatography. A total of 58 samples were analyzed by gas chromatography using a nitrogen-phosphorus detector and routine techniques. For the ELISA test, the samples were diluted to obtain a concentration corresponding to 50% of the absorbance of the standard curve. To determine whether the proximity between the I50 of the standard curve and that of the sample would bring about a more precise result, the samples were divided into three blocks according to the criterion of difference, in modulus, of the I50 of the standard curve and of the I50 of the sample. The samples were classified into three groups. The first was composed of 20 samples with I50 up to 1.5 ng/ml, the second consisted of 21 samples with I50 ranging from 1.51 to 3 ng/ml, and the third of 17 samples with I50 ranging from 3.01 to 13 ng/ml. The determination coefficient (R2 = 0.999) showed that the data obtained by gas chromatography represented a reliable basis. The results obtained by ELISA were also reliable, with an estimated Pearson correlation coefficient of 0.82 between the two methods. This coefficient for the different groups (0.88, 0.79 and 0.49 for groups 1, 2 and 3, respectively) showed greater reliability for the test with dilutions closer to I50.

Effects of caffeine on locomotor activity of horses: determination of the no-effect threshold

Caffeine is the legal stimulant consumed most extensively by the human world population and may be found eventually in the urine and/or blood of race horses. The fact that caffeine is in foods led us to determine the highest no-effect dose (HNED) of caffeine on the spontaneous locomotor activity of horses and then to quantify this substance in urine until it disappeared. We built two behavioural stalls equipped with juxtaposed photoelectric sensors that emit infrared beams that divide the stall into nine sectors in a 'tic-tac-toe' fashion. Each time a beam was interrupted by a leg of the horse, a pulse was generated; the pulses were counted at 5-min intervals and stored by a microcomputer. Environmental effects were minimized by installing exhaust fans producing white noise that obscured outside sounds. One-way observation windows prevented the animals from seeing outside. The sensors were turned on 45 min before drug administration (saline control or caffeine). The animals were observed for up to 8 h after i.v. administration of 2.0, 2.5, 3.0 or 5.0 mg caffeine kg(-1). The HNED of caffeine for stimulation of the spontaneous locomotor activity of horses was 2.0 mg kg(-1). The quantification of caffeine in urine and plasma samples was done by gradient HPLC with UV detection. The no-effect threshold should not be greater than 2.0 microg caffeine ml(-1) plasma or 5.0 microg caffeine ml(-1) urine.

Clenbuterol in the horse: confirmation and quantitation of serum clenbuterol by LC-MS-MS after oral and intratracheal administration

Clenbuterol is a beta2 agonist/antagonist bronchodilator, and its identification in post-race samples may lead to sanctions. The objective of this study was to develop a specific and highly sensitive serum quantitation method for clenbuterol that would allow effective regulatory control of this agent in horses. Therefore, clenbuterol-d9 was synthesized for use as an internal standard, an automated solid-phase extraction method was developed, and both were used in conjunction with a multiple reaction monitoring liquid chromatography-tandem mass spectrometry (LC-MS-MS) method to allow unequivocal identification and quantitation of clenbuterol in 2 mL of serum at concentrations as low as 10 pg/mL. Five horses were dosed with oral clenbuterol (0.8 microg/kg, BID) for 10 days, and serum was collected for 14 days thereafter. Serum clenbuterol showed mean trough concentrations of approximately 150 pg/mL. After the last dose on day 10, serum clenbuterol reached a peak of approximately 500 pg/mL and then declined with a half-life of approximately 7 h. Serum clenbuterol declined to 30 and 10 pg/mL at 48 and 72 h after dosing, respectively. By 96 h after dosing, the concentration was below 4 pg/mL, the limit of detection for this method. Compared with previous results obtained in parallel urinary experiments, the serum-based approach was more reliable and satisfactory for regulation of the use of clenbuterol. Clenbuterol (90 microg) was also administered intratracheally to five horses. Peak serum concentrations of approximately 230 pg/mL were detected 10 min after administration, dropping to approximately 50 pg/mL within 30 min and declining much more slowly thereafter. These observations suggest that intratracheal administration of clenbuterol shortly before race time can be detected with this serum test. Traditionally, equine drug testing has been dependent on urine testing because of the small volume of serum samples and the low concentrations of drugs found therein. Using LC-MS-MS testing, it is now possible to unequivocally identify and quantitate low concentrations (10 pg/mL) of drugs in serum. Based on the utility of this approach, the speed with which new tests can be developed, and the confidence with which the findings can be applied in the forensic situation, this approach offers considerable scientific and regulatory advantages over more traditional urine testing approaches.

Ropivacaine in the horse: its pharmacological responses, urinary detection and mass spectral confirmation

This report evaluates the pharmacological responses, urinary detection and mass spectral confirmation of ropivacaine in horses. Ropivacaine, a potent local anesthetic (LA) recently introduced in human medicine, has an estimated highest no-effect dose (HNED) of about 0.4 mg/site as determined in our abaxial sesamoid block model. Apparent ropivacaine equivalents were detectable by ELISA screening using a mepivacaine ELISA test after administration of clinically effective doses. Mass spectral examination of postadministration urine samples showed no detectable parent ropivacaine, but a compound indistinguishable from authentic 3-hydroxyropivacaine was recovered from these samples. The study shows that ropivacaine is a potent LA in the horse, that clinically effective doses can be detected in postadministration samples by ELISA-based screening, and that its major post administration urinary metabolite is 3-hydroxyropivacaine.

Clenbuterol in the horse: urinary concentrations determined by ELISA and GC/MS after clinical doses

Clenbuterol is a beta2 agonist/antagonist bronchodilator marketed as Ventipulmin and is the only member of this group of drugs approved by the US Food and Drug Administration (FDA) for use in horses. Clenbuterol is a class 3 drug in the Association of Racing Commissioners International (ARCI) classification system; therefore, its identification in postrace samples may lead to sanctions. Recently, the sensitivity of postrace testing for clenbuterol has been substantially increased. The objective of this study was to determine the 'detection times' for clenbuterol after administration of an oral clinical dose (0.8 g/kg, b.i.d.) of Ventipulmin syrup. Five horses received oral clenbuterol (0.8 g/kg, b.i.d.) for 10 days, and urine concentrations of clenbuterol were determined by an enhanced enzyme-linked immunoabsorbent assay (ELISA) test and gas chromatography/mass spectrometric (GC/MS) analysis by two different methods for 30 days after administration. Twenty-four hours after the last administration, urine concentrations of apparent clenbuterol, as measured by ELISA, averaged about 500 ng/mL, dropping to about 1 ng/mL by day 5 posttreatment. However, there was a later transient increase in the mean concentrations of apparent clenbuterol in urine, peaking at 7 ng/mL on day 10 postadministration. The urine samples were also analysed using mass spectral quantification of both the trimethylsilyl (TMS) and methane boronic acid (MBA) derivatives of clenbuterol. Analysis using the TMS method showed that, at 24 h after the last administration, the mean concentration of recovered clenbuterol was about 22 ng/mL. Thereafter, clenbuterol concentrations fell below the limit of detection of the TMS-method by day 5 after administration but became transiently detectable again at day 10, with a mean concentration of about 1 ng/mL. Derivatization with MBA offers significant advantages over TMS for the mass spectral detection of clenbuterol, primarily because MBA derivatization yields a high molecular weight base peak of 243 m/z, which is ideal for quantitative purposes. Therefore, mass spectral analyses of selected urine samples, including the transient peak on day 10, were repeated using MBA derivatization, and comparable results were obtained. The results show that clenbuterol was undetectable in horse urine by day 5 after administration. However, an unexpected secondary peak of clenbuterol was observed at day 10 after administration that averaged approximately 1 ng/mL. Because of this secondary peak, the detection time for clenbuterol (0.8 g/kg, b.i.d. x 10 days) is at least 11 days if the threshold for detection is set at 1 ng/mL.

Intratracheal clenbuterol in the horse: its pharmacological efficacy and analytical detection

Clenbuterol, a beta2 agonist/antagonist, is the only bronchodilator approved by the US Food and Drug Administration for use in horses. The Association of Racing Commissioners International classifies clenbuterol as a class 3 agent, and, as such, its identification in post-race samples may lead to sanctions. Anecdotal reports suggest that clenbuterol may have been administered by intratracheal (IT) injection to obtain beneficial effects and avoid post-race detection. The objectives of this study were (1) to measure the pharmacological efficacy of IT dose of clenbuterol and (2) to determine the analytical findings in urine in the presence and absence of furosemide. When administered intratracheally (90 microg/horse) to horses suffering from chronic obstructive pulmonary disease (COPD), clenbuterol had effects that were not significantly different from those of saline. In parallel experiments using a behavior chamber, no significant effects of IT clenbuterol on heart rate or spontaneous locomotor activity were observed. Clenbuterol concentrations in the urine were also measured after IT dose in the presence and absence of furosemide. Four horses were administered i.v. furosemide (5 mg/kg), and four horses were administered saline (5 mL). Two hours later, all horses were administrated clenbuterol (IT, 90 microg), and the furosemide-treated horses received a second dose of furosemide (2.5 mg/kg, i.v.). Three hours after clenbuterol dose (1 h after hypothetical 'post-time'), the mean specific gravity of urine samples from furosemide-treated horses was 1.024, well above the 1.010 concentration at which furosemide is considered to interfere with drug detection. There was no interference by furosemide with 'enhanced' ELISA screening of clenbuterol equivalents in extracted and concentrated samples. Similarly, furosemide had no effect on mass spectral identification or quantification of clenbuterol in these samples. These results suggest that the IT dose of clenbuterol (90 microg) is, in pharmacological terms, indistinguishable from the dose of saline, and that, using extracted samples, clenbuterol dose is readily detectable at 3 h after dosing. Furthermore, concomitant dose of furosemide does not interfere with detection or confirmation of clenbuterol.

Identification of lidocaine and its metabolites in post-administration equine urine by ELISA and MS/MS

Lidocaine is a local anesthetic drug that is widely used in equine medicine. It has the advantage of giving good local anesthesia and a longer duration of action than procaine. Although approved for use in horses in training by the American Association of Equine Practitioners (AAEP), lidocaine is also an Association of Racing Commissioners International (ARCI) Class 2 drug and its detection in forensic samples can result in significant penalties. Lidocaine was observed as a monoprotonated ion at m/z 235 by ESI+ MS/MS (electrospray ionization-positive ion mode) analysis. The base peak ion at m/z 86, representing the postulated methylenediethylamino fragment [CH2N(CH2CH3)2]+, was characteristic of lidocaine and 3-hydroxylidocaine in both ESI+ and EI (electron impact-positive ion mode) mass spectrometry. In addition, we identified an ion at m/z 427 as the principal parent ion of the ion at m/z 86, consistent with the presence of a protonated analog of 3-hydroxylidocaine-glucuronide. We also sought to establish post-administration ELISA-based 'detection times' for lidocaine and lidocaine-related compounds in urine following single subcutaneous injections of various doses (10, 40, 400 mg). Our findings suggest relatively long ELISA based 'detection times' for lidocaine following higher doses of this drug.

Identification of hydroxyropivacaine glucuronide in equine urine by ESI+/MS/MS

Ropivacaine is a local anesthetic that has a high potential for abuse in racing horses. It can be recovered from urine collected after administration as a hydroxylated metabolite following beta-glucuronidase treatment of the urine. Based on these findings, it has been inferred that ropivacaine is present in equine urine as a glucuronide metabolite; however, these metabolites have never been directly identified. Using ESI+/MS/MS, the presence of a [M+H]+ molecular ion of m/z 467 was demonstrated in urine corresponding to the calculated mass of a hydroxyropivacaine glucuronide +1. The abundance of this ion diminished after glucuronidase treatment with concomitant appearance of a m/z 291 peak, which is consistent with its hydrolysis to hydroxyropivacaine. In further work, the m/z 467 material was fragmented in the MS/MS system, yielding fragments interpretable as hydroxyropivacaine glucuronide. These data are consistent with the presence of a hydroxyropivacaine glucuronide in equine urine and constitute the first direct demonstration of a specific glucuronide metabolite in equine urine.

Remifentanil in the horse: identification and detection of its major urinary metabolite

Remifentanil (4-methoxycarbonyl-4-[(1-oxopropyl)phenylamino]-1-piperidinepropionic acid methyl ester) is a mu-opioid receptor agonist with considerable abuse potential in racing horses. The identification of its major equine urinary metabolite, 4-methoxycarbonyl-4-[(1-oxopropyl)phenylamino]-1-piperidinepropionic+ ++ acid, an ester hydrolysis product of remifentanil is reported. Administration of remifentanil HCl (5 mg, intravenous) produced clear-cut locomotor responses, establishing the clinical efficacy of this dose. ELISA analysis of postadministration urine samples readily detected fentanyl equivalents in these samples. Mass spectrometric analysis, using solid-phase extraction and trimethylsilyl (TMS) derivatization, showed the urine samples contained parent remifentanil in low concentrations, peaking at 1 h. More significantly, a major peak was identified as representing 4-methoxycarbonyl-4-[(1-oxopropyl)phenylamino]-1-piperidinepropionic+ ++ acid, arising from ester hydrolysis of remifentanil. This metabolite reached its maximal urinary concentrations at 1 h and was present at up to 10-fold greater concentrations than parent remifentanil. Base hydrolysis of remifentanil yielded a carboxylic acid with the same mass spectral characteristics as those of the equine metabolite. In summary, these data indicate that remifentanil administration results in the appearance of readily detectable amounts of 4-methoxycarbonyl-4-[(1-oxopropyl)phenylamino]-1-piperidinepropionic+ ++ acid in urine. On this basis, screening and confirmation tests for this equine urinary metabolite should be optimized for forensic control of remifentanil.

Direct MS-MS identification of isoxsuprine-glucuronide in post-administration equine urine

Isoxsuprine is routinely recovered from enzymatically-hydrolyzed, post-administration urine samples as parent isoxsuprine in equine forensic science. However, the specific identity of the material in horse urine from which isoxsuprine is recovered has never been established, although it has long been assumed to be a glucuronide conjugate (or conjugates) of isoxsuprine. Using ESI/MS/MS positive mode as an analytical tool, urine samples collected 4-8 h after isoxsuprine administration yielded a major peak at m/z 554 that was absent from control samples and resisted fragmentation to daughter ions. Titration of this material with increasing concentrations of sodium acetate yielded m/z peaks consistent with the presence of monosodium and disodium isoxsuprine-glucuronide complexes, suggesting that the starting material was a dipotassium-isoxsuprine-glucuronide complex. Electrospray ionization mass spectrometry negative mode disclosed the presence of a m/z 476 peak that declined following enzymatic hydrolysis and resulted in the concomitant appearance of peaks at m/z 300 and 175. The resulting peaks were consistent with the presence of isoxsuprine (m/z 300) and a glucuronic acid residue (m/z 175). Examination of the daughter ion spectrum of this putative isoxsuprine-glucuronide m/z 476 peak showed overlap of many peaks with those of similar spectra of authentic morphine-3- and morphine-6-glucuronides, suggesting they were derived from glucuronic acid conjugation. These data suggest that isoxsuprine occurs in post-administration urine samples as an isoxsuprine-glucuronide conjugate and also, under some circumstances, as an isoxsuprine-glucuronide-dipotassium complex.

Effect of amitraz and xylazine on some physiological variables of horses

The effect of the intravenous injection of amitraz (0.1mg/kg) to horses on cardiac activity, respiratory rate, intestinal motor activity, rectal temperature, sweating and masticating was evaluated and compared to the effect of intravenous administration of xylazine (1mg/kg, iv) on heart rate, respiratory rate and intestinal activity. Amitraz caused a significant decrease in heart activity, respiratory rate and intestinal movements, but these effects were not as pronounced as those caused by xylazine. Amitraz also caused a significant relaxation of the rectal smooth muscle, and an apparent increase in sweating and in the frequency of horses found masticating hay. Rectal temperature was not influenced by amitraz. The results indicated that amitraz, at the dose used, did not cause severe side effects in horses.

Diclazuril in the horse: its identification and detection and preliminary pharmacokinetics

Diclazuril (4-chlorophenyl [2,6-dichloro-4-(4,5-dihydro-3H-3,5-dioxo-1,2,4-triazin-2-yl)pheny l] acetonitrile), is a benzeneacetonitrile antiprotozoal agent (Janssen Research Compound R 64433) marketed as Clinacox . Diclazuril may have clinical application in the treatment of Equine Protozoal Myeloencephalitis (EPM). To evaluate its bioavailability and preliminary pharmacokinetics in the horse we developed a sensitive quantitative high-pressure liquid chromatography (HPLC) method for diclazuril in equine biological fluids. MS/MS analysis of diclazuril in our HPLC solvent yielded mass spectral data consistent with the presence of diclazuril. After a single oral dose of diclazuril at 2.5 g/450 kg (as 500 g Clinacox), plasma samples from four horses showed good plasma concentrations of diclazuril which peaked at 1.077 +/- 0.174 microg/mL (mean +/- SEM) with an apparent plasma half-life of about 43 h. When this dose of Clinacox was administered daily for 21 days to two horses, mean steady state plasma concentrations of 7-9 microg/mL were attained. Steady-state levels in the CSF ranged between 100 and 250 ng/mL. There was no detectable parent diclazuril in the urine samples of dosed horses by HPLC or by routine postrace thin layer chromatography (TLC). These results show that diclazuril is absorbed after oral administration and attains steady-state concentrations in plasma and CSF. The steady state concentrations attained in CSF are more than sufficient to interfere with Sarcocystis neurona, whose proliferation is reportedly 95% inhibited by concentrations of diclazuril as low as 1 ng/mL. These results are therefore entirely consistent with and support the reported clinical efficacy of diclazuril in the treatment of clinical cases of EPM.

Pharmacokinetics and therapeutic efficacy of rimantadine in horses experimentally infected with influenza virus A2

OBJECTIVE

To determine pharmacokinetics of single and multiple doses of rimantadine hydrochloride in horses and to evaluate prophylactic efficacy of rimantadine in influenza virus-infected horses.

ANIMALS

5 clinically normal horses and 8 horses seronegative to influenza A.

PROCEDURE

Horses were given rimantadine (7 mg/kg of body weight, i.v., once; 15 mg/kg, p.o., once; 30 mg/kg, p.o., once; and 30 mg/kg, p.o., q 12 h for 4 days) to determine disposition kinetics. Efficacy in induced infections was determined in horses seronegative to influenza virus A2. Rimantadine was administered (30 mg/kg, p.o., q 12 h for 7 days) beginning 12 hours before challenge-exposure to the virus.

RESULTS

Estimated mean peak plasma concentration of rimantadine after i.v. administration was 2.0 micrograms/ml, volume of distribution (mean +/- SD) at steady-state (Vdss) was 7.1 +/- 1.7 L/kg, plasma clearance after i.v. administration was 51 +/- 7 ml/min/kg, and beta-phase half-life was 2.0 +/- 0.4 hours. Oral administration of 15 mg of rimantadine/kg yielded peak plasma concentrations of < 50 ng/ml after 3 hours; a single oral administration of 30 mg/kg yielded mean peak plasma concentrations of 500 ng/ml with mean bioavailability (F) of 25%, beta-phase half-life of 2.2 +/- 0.3 hours, and clearance of 340 +/- 255 ml/min/kg. Multiple doses of rimantadine provided steady-state concentrations in plasma with peak and trough concentrations (mean +/- SEM) of 811 +/- 97 and 161 +/- 12 ng/ml, respectively. Rimantadine used prophylactically for induced influenza virus A2 infection was associated with significant decreases in rectal temperature and lung sounds.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of rimantadine to horses can safely ameliorate clinical signs of influenza virus infection.

Bupivacaine in the horse: relationship of local anaesthetic responses and urinary concentrations of 3-hydroxybupivacaine

Bupivacaine is a potent local anaesthetic used in equine medicine. It is also classified as a Class 2 foreign substance by the Association of Racing Commissioners International (ARCI). The identification of residues in postrace urine samples may cause regulators to impose significant penalties. Therefore, an analytical/pharmacological database was developed for this medication. The highest no-effect dose (HNED) for the local anaesthetic effect of bupivacaine was determined to be 0.25 mg by using an abaxial sesamoid local anaesthetic model. Administration of the HNED of bupivacaine to eight horses yielded a peak urine concentration of apparent bupivacaine of 23.3 ng/mL 2 h after injection as determined with enzyme-linked immunosorbent assay (ELISA) screening. The major metabolite recovered from beta-glucuronidase-treated equine urine after dosing with bupivacaine is a hydroxybupivacaine, either 3-hydroxybupivacaine, 4-hydroxybupivacaine, or a mixture of the two. To determine which positional isomer occurs in the horse, 4-hydroxybupivacaine was obtained from Maxxam Analytics, Inc., and 3-hydroxybupivacaine was synthesized, purified, and characterized. Furthermore, a quantitative mass spectrometric method was developed for the metabolite as recovered from horse urine. Following subcutaneous injection of the HNED of bupivacaine, the concentration of the hydroxybupivacaine recovered from horse urine reached a peak of 27.4 ng/mL at 4 h after administration as measured by gas chromatography/mass spectrometry (GC/MS). It was also unequivocally demonstrated with ion chromatography that the hydroxybupivacaine metabolite found in horse urine is exclusively 3-hydroxybupivacaine and not 4-hydroxybupivacaine. The mean pH of the 4-h urine samples was 7.21; the mean urine creatinine was 209.5 mg/dL; and the mean urine specific gravity was 1.028. There was no apparent effect of pH, urine creatinine concentration, or specific gravity on the concentration of 3-hydroxybupivacaine recovered. The concentration of bupivacaine or its metabolites after administration of a HNED dose are detectable by mass spectrometric techniques. This study also suggests that recovery of concentrations less than approximately 30 ng/mL of 3-hydroxybupivacaine from postrace urine samples is unlikely to be associated with a recent local anaesthetic effect of bupivacaine.

Testing for therapeutic medications: analytical/pharmacological relationships and limitations' on the sensitivity of testing for certain agents

Proper veterinary care of horses requires that horses in training have access to modern therapeutic medication. However, the sensitivity of equine drug testing now allows for detection of pharmacologically insignificant concentrations of many therapeutic medications. In 1995, the Association of Racing Commissioners International (ARCI) resolved that members 'address trace level detection so as not to lead to disciplinary action based on pharmacologically insignificant traces of these substances'. The rationale behind this approach is to prevent overly-sensitive testing from inhibiting the proper and appropriate veterinary care of performance horses. This review describes a scientific approach to implement this resolution using local anaesthetics as a model system and compares this approach with others currently in place. For the purpose of this discussion, a 'trace' concentration is defined as a pharmacologically-insignificant concentration. Initially, the target pharmacological effect (e.g. local anaesthesia) was identified, and the dose response relationship was quantified. The 'Highest No Effect Dose' (HNED) was estimated and then administered to horses. Next, the target analyte was identified, synthesized, if necessary, and quantified in blood or urine; the concentrations observed after administration of the HNED are, by definition, true concentrations and hence are pharmacologically insignificant. The key to this approach has been the synthesis of a unique series of authentic equine metabolite standards, which has allowed scientific identification of the concentration at which the pharmacological effect was indistinguishable from control values. Traces found at less than this concentration are, by definition, 'no effect limits', 'no effect traces' (NETs), 'no effect cut-offs', 'no effect limitations on the sensitivity of testing', or 'subtherapeutic residues'. Conversely, this approach will also identify potent medications for which the sensitivity of testing may need to be improved. Within the context of these experiments, the data create an analytical/pharmacological database that should assist industry professionals in interpreting the significance of trace concentrations of these medications or their metabolites in official samples. The most favourable outcome of this research is more medically appropriate use of therapeutic medications in performance horses, yielding substantial benefits to the health and welfare of these horses.

Mepivacaine: its pharmacological effects and their relationship to analytical findings in the horse

Mepivacaine is a local anaesthetic drug that is widely used in equine medicine and is classified by the Association of Racing Commissioners International (ARCI) as a Class 2 foreign substance that may cause regulators to impose significant penalties if residues are identified in post-race urine samples. Therefore, an analytical/pharmacological database was developed for this agent and its metabolites. Using an abaxial sesamoid local anaesthetic model, it was determined that the highest no-effect dose (HNED) for its local anaesthetic effect was 2 mg. Using enzyme-linked immunosorbent assay (ELISA) screening, it was determined that subcutaneous (s.c.) administration of the HNED of mepivacaine to eight horses yielded a peak urinary concentration of apparent mepivacaine of 63 ng/mL 2 h after injection. The major identified metabolite recovered from equine urine after dosing with mepivacaine is 3-hydroxymepivacaine. Therefore, 3-hydroxymepivacaine was synthesized, purified and characterized, and a quantitative mass spectrometric method was developed for this metabolite as isolated from horse urine. Following subcutaneous injection of the HNED of mepivacaine, the concentration of 3-hydroxymepivacaine recovered from horse urine reached a peak of about 64.6 ng/mL at 4 h after administration as measured by GC/MS. The concentration of mepivacaine or its metabolites after administration of a HNED dose are detectable by mass spectral techniques. Within the limits of this research, the study suggests that recovery of concentrations less than about 65 ng/mL of 3-hydroxymepivacaine from post-race urine samples may not be associated with a recent LA effect of mepivacaine.

Lack of local anaesthetic efficacy of fentanyl in the abaxial sesamoid block model

Fentanyl and other opioid drugs have their effect in the central nervous system; however, activity at peripheral sites has also been demonstrated. Pain-suppression activity at peripheral sites raises the possibility of skilled individuals producing local anaesthetic effects with small doses of opioid drugs that would be difficult to detect forensically and could be used to affect the outcome of a race. Therefore, the local pain-suppression effect (peripheral nerve inhibition) of fentanyl was tested using an abaxial sesamoid block/hoof withdrawal model. With this model, fentanyl did not produce significant anaesthesia when tested in eight Thoroughbred horses. This suggests that fentanyl at this or lower doses is unlikely to reduce pain perception when applied directly to sensory neurons. However, the effect of fentanyl and other opioids on joint pain perception of horses, especially inflamed joints, is unknown.

Lidocaine in the horse: its pharmacological effects and their relationship to analytical findings

Lidocaine is a local anaesthetic agent that is widely used in equine medicine. It is also an Association of Racing Commissioners International (ARCI) Class 2 foreign substance that may cause regulators to impose substantial penalties if residues are identified in post race urine samples. Therefore, an analytical/pharmacological database was developed for this drug. Using our abaxial sesamoid local anaesthetic model, the highest no-effect dose (HNED) for the local anaesthetic effect of lidocaine was determined to be 4 mg. Using enzyme-linked immunosorbent assay (ELISA) screening, administration of the HNED of lidocaine to eight horses yielded peak serum and urine concentrations of apparent lidocaine of 0.84 ng/mL at 30 min and 72.8 ng/mL at 60 min after injection, respectively. These concentrations of apparent lidocaine are readily detectable by routine ELISA screening tests (LIDOCAINE ELISA, Neogen, Lexington, KY). ELISA screening does not specifically identify lidocaine or its metabolites, which include 3-hydroxylidocaine, dimethylaniline, 4-hydroxydimethylaniline, monoethylglycinexylidine, 3-hydroxymonoethylglycinexylidine, and glycinexylidine. As 3-hydroxylidocaine is the major metabolite recovered from equine urine, it was synthesized, purified and characterized, and a quantitative mass spectrometric method was developed for 3-hydroxylidocaine as recovered from horse urine. Following subcutaneous (s.c.) injection of the HNED of lidocaine, the concentration of 3-hydroxylidocaine recovered from urine reached a peak of about 315 ng/mL at 1 h after administration. The mean pH of the 1 h post dosing urine samples was 7. 7, and there was no apparent effect of pH on the amount of 3-hydroxylidocaine recovered. Within the context of these experiments, the data suggests that recovery of less than 315 ng/mL of 3-hydroxylidocaine from a post race urine sample is unlikely to be associated with a recent local anaesthetic effect of lidocaine. Therefore these data may be of assistance to industry professionals in evaluating the significance of small concentrations of lidocaine or its metabolites in postrace urine samples. It should be noted that the quantitative data are based on analytical methods developed specifically for this study, and that methods used by other laboratories may yield different recoveries of urine 3-hydroxylidocaine.

Characterization of the antinociceptive and sedative effect of amitraz in horses

Amitraz, an acaricide used to control ectoparasites in animals has a complex pharmacological activity, including alpha2-adrenergic agonist action. The purpose of this research was to investigate the possible antinociceptive and/or sedative effect of amitraz in horses. The sedative effect of the intravenous (i.v.) injection of dimethylformamide (DMF, 5 mL, control) or amitraz (0.05, 0.10, 0.15 mg/kg), was investigated on the head ptosis test. The participation of alpha2-adrenergic receptors in the sedative effect provoked by amitraz was studied by dosing yohimbine (0.12 mg/kg, i.v.). To measure the antinociception, xylazine hydrochloride (1 mg/kg, i.v., positive control) and the same doses of amitraz and DMF were used. A focused radiant light/heat directed onto the fetlock and withers of a horse were used as a noxious stimulus to measure the hoof withdrawal reflex latency (HWRL) and the skin twitch reflex latency (STRL). The three doses of amitraz used (0.05, 0.10 and 0.15 mg/kg) provoked a dose-dependent relaxation of the cervical muscles. The experiments with amitraz and xylazine on the HWRL showed that after i.v. administration of all doses of amitraz there was a significant increase of HWRL up to 150 min after the injections. Additionally, there was a significant difference between control (DMF) and positive control (xylazine) values up to 30 min after drug injection. On the other hand, the experiments on the STRL show that after administration of amitraz at the dose of 0.15 mg/kg, a significant increase in STRL was observed when compared with the control group. This effect lasted up to 120 min after injection. However, no significant antinociceptive effect was observed with the 0.05 and 0.10 mg/kg doses of amitraz or at the 1.0 mg/kg dose of xylazine.