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Detection of Various Performance Enhancing Substances in Specimens Collected from Race Horses in Illinois: A Five-Year Experience* Lisa Taddei, Marc Benoit, Andre Sukta, Joshua Peterson, R.E. Gaensslen, and Adam Negrusz† Animal Forensic Toxicology Laboratory, University of Illinois at Chicago, 2242 West Harrison Street, Chicago, Illinois 60612
Abstract In order to protect the integrity of horse racing in Illinois, a complex testing of urine and blood specimens collected post-race from winning and special designation horses is continuously conducted. The initial screening by immunoassays was followed by the confirmation on presumptive positive samples. Instrumental screening was also conducted. Perimortem and postmortem specimens and special exhibits (syringes, needles, etc.) were also analyzed. The administration of alkalinizing agents was detected by measuring the total plasma carbon dioxide concentration. The laboratory analyzed specimens collected post race from winning horses and special designation horses at eight race tracks in the State of Illinois over the five-year time period (2004–2009). The total number of specimens collected was 91,808, comprising 45,210 urine specimens and 46,598 blood specimens. The total number of violations was 413 (0.45% of the total number of specimens analyzed); 207 were blood specimens (0.44% of the total blood specimens analyzed), and 206 were urine specimens (0.45% of the total urine specimens analyzed). A total of 220 violations were reported for harness horses, and 193 were reported for Thoroughbred horses. The number of reported violations of the total tested specimens in Illinois was small, but a wide variety of performance-enhancing drugs was shown.
Introduction One of the most important objectives of each horseracing jurisdiction is to protect the integrity of the sport through the administration of a multifaceted control of the use of substances that have a potential to enhance a horse’s performance in a race. The drugs and substances that have been identified as per-
* This work was presented at the 2011 AAFS meeting in Chicago, Illinois. † Author to whom correspondence should be addressed. Email:
[email protected].
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formance enhancing have been completely and comprehensively classified based upon pharmacological activity. Within these guidelines the Association of Racing Commissioners International (ARCI) has established five classes of performance enhancing substances ranging from Class 1 Substances, those demonstrating the greatest potential to enhance performance, to Class 5 Substances, those demonstrating the least potential for enhancing performance (1). The ARCI definitions for each class follows. Class 1: Stimulant and depressant drugs that have the highest potential to affect performance and that have no generally accepted medical use in the racing horse. Many of these agents are Drug Enforcement Administration Schedule II substances. Examples include opioids, cocaine, and amphetamines. Class 2: Includes drugs that have a high potential to affect performance, but less than those drugs in Class 1. Drugs in Class 2 are 1. not generally accepted as therapeutic agents in racing horses or 2. therapeutic agents that have a high potential for abuse. Class 3: Drugs in that group may or may not have generally accepted medical use in the racing horse, but the pharmacology of which suggests less potential to affect performance than drugs in Class 2. Examples include anabolic steroids, bronchodilators, local anesthetic, or high-ceiling (loop) diuretics. Class 4: This class includes therapeutic medications that have less potential to affect performance than those in Class 3. Examples of drugs in this class include less potent diuretics acting at distal convoluted tubule (e.g., chlorothiazide), or acting at collecting duct system (e.g., spironolactone), corticosteroids, antihistamines, or skeletal muscle relaxants without prominent central nervous system effects, non-steroidal antiinflammatory drugs (NSAIDs), and others. Class 5: This class includes those therapeutic medications for which concentration limits have been established by the racing jurisdictions, as well as certain miscellaneous agents such as dimethyl sulfoxide (DMSO) and other medications as deter-
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mined by the regulatory bodies. Included specifically are agents that have very localized actions only, such as anti-ulcer drugs, and certain anti-allergic drugs. The anticoagulant drugs are also included. The ARCI guidelines were developed to aid in the interpretation of racehorse drug-screening results and include suggested penalties for each class violation. These guidelines were also designed to give racing authorities, such as racing regulators or stewards, a framework within which they can evaluate the relative performance enhancing effects of various drugs and substances and the associated impact that a drug or substance may be anticipated to have on the outcome of a race (2). The penalty guidelines allow for mitigating circumstances to be taken into account when the racing authorities issue a ruling dictated by the Illinois Administrative Code (3). A penalty in Illinois may include anything from a small fine, to the monetary prize (purse money) redistribution, to, in the most severe cases, a racing ban. All Illinois Racing Board rules and regulations regarding the administration of medication and testing for the presence of performance enhancing drugs are published in the General Assembly's Illinois Administrative Code, Part 603 Medication (3). The Rule lists threshold concentrations for medications permitted for therapeutic administration in blood (serum, plasma) such as phenylbutazone, furosemide, flunixin, ketoprofen, selected anabolic steroids (testosterone, boldenone, nandrolone, stanozolol), thresholds for selected medications in urine (e.g., isoxsuprine, DMSO, anabolic steroids), as well as Odesmethylpyrilamine (pyrilamine metabolite) and benzoylecgonine (cocaine metabolite). The Rule also requires testing for the use of alkalinizing agents, such as sodium bicarbonate, the employment of which is referred to as “milkshaking”. The use of alkalinizing agents is revealed by measuring the total carbon dioxide (TCO2) concentration in plasma (4–6). The list of all thresholds is presented in Table I. There is a “zero toler-
Table I. Threshold Concentrations for Selected Compounds in Specimens Collected from Race Horses in Illinois Substance
Specimen
Threshold
Phenylbutazone and/or metabolite (oxyphenylbutazone)
Serum
5 µg/mL
Furosemide
Serum
100 ng/mL
Total Carbon dioxide
Plasma
37 mmol/L
Flunixin
Serum
20 ng/mL
Ketoprofen
Serum
10 ng/mL
Benzoylecgonine (cocaine metabolite)
Urine
150 ng/mL*
DMSO
Urine
500 µg/mL
Isoxsuprine
Urine
1000 ng/mL
Pyrilamine
Urine
50 ng/mL
* Every concentration equal to or greater than the LOQ is reported as a violation. Levels equal to or greater than the threshold are associated with more severe penalties.
ance” established for Class 1–3 drugs. If Class 4 or 5 drugs are detected in a specimen, quantitation of all relevant drugs must be performed and the subsequent results reported to the Illinois Racing Board Legal Council, state veterinarians, and stewards. The only comprehensive literature report on drug use in racing dates from the 12-year period between 1970 through 1981 (7). This paper describes the principles of equine testing for performance-enhancing substances, including allowed medications, and presents a summary of analytical findings on all winning racehorses obtained during the five-year period (2004 through 2009) in Illinois, the most frequently encountered drug violations, and drug use trends in general.
Methods Specimen collection from race horses
The Animal Forensic Toxicology Laboratory analyzed a total of 91,808 specimens, 45,210 urine specimens and 46,598 blood specimens, collected from Thoroughbred and harness horses at eight race tracks in Illinois over the five-year time period from July 2004 through June 2009. The results from only seven race tracks are presented in this report because no violations were recorded on one track. Blood samples were drawn only by the State Veterinarian after checking the horses’ identification tattoos. Blood from horses was collected to 13-mL serum separator and 4.5 plasma-separator Vacutainer tubes. Plasma samples were collected for the TCO2 and erythropoietin (EPO) analysis. According to the current testing protocol in Illinois, only harness horses are tested for the use of alkalinizing agents, with the exception of graded stakes races. The main argument for testing harness horses and not Thoroughbred for TCO2 is the belief that this type of blood doping will only provide a benefit to horses competing in endurance races. A “graded stakes race” term was adopted nationwide by the Thoroughbred Owners and Breeders Association (TOBA) to Thoroughbred horse races where the stake, or entry fee, must be paid by owners. The race track then adds an additional amount which constitutes the total amount of prize money to be paid to the first, second, third, and typically fourth place finishers. These races provide approximately 100 blood and urine samples for analysis in Illinois annually. No elevated TCO2 plasma concentrations were encountered during the 2004–2009 time period. The horse’s name (later covered by a seal to hide information from the laboratory personnel), race number, and winner/special designation were written on the permanent label of the blood tubes. Special designation horses are usually the second or third place finishers selected by stewards or state veterinarians for random drug testing. Some equine athletes may also be flagged for drug testing because of unusual behavior or surrounding circumstances. After specimen collection, the blood tubes were placed upright in a tube rack for between 15 to 30 min to allow for blood clotting to progress and then centrifuged for 15 min to allow phase separation to occur. Following the separation of
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serum or plasma and red blood cells in the centrifuge, each blood tube was sealed by the Chief Veterinary Technician. One serum and one plasma tube from each set was marked as a referee specimen; the remaining samples were marked as laboratory samples. Once sealed, the tubes were placed in the locked refrigerator and held there until placed in the sealed sample box for shipment to the laboratory. Urine samples were collected by the State Veterinary Technicians using a long-handled plastic cup lined with a disposable plastic collection bag. The natural void urine from the horse was collected in the secured stall area. Following sample collection, the urine sample was transferred from the disposable plastic liner bag into two plastic urine containers in equal portions and sealed. One container was marked as laboratory, and the other as a referee sample. According to the Illinois Rule, when an unauthorized substance or an overage of an authorized medication is detected in a laboratory sample, the horse owner, trainer, or other person charged with a violation has an opportunity to request that the referee sample be opened and a split portion sent to another laboratory to verify the positive test. The remaining portion of a referee sample shall be preserved by the laboratory in case further testing is requested (3). When all blood and urine samples had been collected for the day’s racing program, they were placed in a shipping container along with the proper paperwork, sealed, and shipped to the laboratory according to the chain-of-custody procedures.
false-positive results, a very high cost per test, or there is no commercially available kit. For the above reasons the instrumental screening was also performed employing the established solid-phase or solvent extraction procedures followed by gas chromatography–mass spectrometry (GC–MS) (e.g., DMSO analysis), or ion trap or triple-quadrupole liquid chromatography (LC)–MS (e.g., anabolic steroids analysis) methods. All samples selected by instrumental screening as presumptive positive were reanalyzed by either the same method with the different scan mode parameters, or by different instrumental technique. For anabolic steroids, for example, the initial LC– MS–MS analysis was performed using one ion transition. In the second analysis, at least five transitions were considered for drug identification. Positive drug identification was always based on analysis of at least two portions of the original sample. In addition, the identification of a substance always comprised a direct comparison with a reference standard added to a corresponding naïve biological specimen and analyzed in series with the test sample. Confirmation
All presumptive positive samples selected by ELISA screening were subsequently confirmed by GC–MS or LC– MS(–MS) methods according to the standard operating procedures (SOPs). All quantitative analyses were also performed according to the respective SOPs.
Perimortem and postmortem samples
The Animal Forensic Toxicology Laboratory analyzed a total of 302 blood samples collected from animals awaiting euthanization (perimortem) or postmortem over the five-year time period (2004 through 2009). Special exhibits
Over the five-year period of time (2004–2009) the Animal Forensic Toxicology Laboratory analyzed 116 specimens identified as special exhibits. These were items such as syringes, needles, neat drugs, empty containers and vials, liquids, plastic bags found on race courses and adjacent properties and/or confiscated from persons within the surrounding confines of racecourses by racing authorities and subsequently delivered under chain of custody to the laboratory for analysis.
Table II. Total Number of Specimens Tested and Percentage of Reported Violations in Blood and Urine (2004–2009) Specimen
Number of Samples
Percentage of Total
Blood
46,598
50.7
Urine
45,210
49.3
Total
91,808
100
Violations in blood
207
0.44
Violations in urine
206
0.45
Total violations (blood, urine)
413
0.45
Initial screening
All urine and blood samples collected post-race from winning horses in Illinois were initially screened for the presence of performance enhancing substances by using at least 65 commercially available enzyme-linked immunosorbent assay (ELISA) kits. The laboratory uses group-specific ELISA kits designed to detect several drugs within one pharmacological group (e.g., bronchodilators, antihistamines, opioids) and a single analyte (e.g., indometacin-specific kit). The laboratory also screened the specimens collected perimortem, postmortem, and the special exhibits for the presence of prohibited substances. The initial screening in equine testing cannot always be performed by employing immunochemical methodologies including ELISA. The main reasons include insufficient sensitivity of available kits, a high percentage of
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Table III. Number of Perimortem and Postmortem Samples and Special Exhibits Tested (2004–2009) Year
Perimortem/Postmortem
Special Exhibits
2005
51
19
2006
57
21
2007
72
8
2008
67
1
2009
55
67
Total
302
116
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The use of alkalinizing agents, such as sodium bicarbonate, was revealed primarily by means of the measurement of the plasma TCO2 concentration as well as the additional information provided by measuring plasma total proteins and the ion concentrations for K+, Na+, Cl–, and Ca+2. The analysis was performed according to the existing SOP by using Beckman SYNCHRON EL-ISE® instrument, and since January 1, 2009, the laboratory has been performing these analyses using the Beckman Coulter DxC 600 analyzer. If the initial TCO2 measurement in the laboratory portion of plasma indicated an elevated concentration (equal to or higher than 37 mmol/L), it was the Illinois Racing Board recommendation that the referee portion of plasma sample be opened and analyzed by the laboratory.
other countries over varying periods between 1975 and 1981 (7). The proportion of positive results found in that study was one in 400 (0.25%) for both winning and non-winning horses. Drugs such as methylxanthines, NSAIDs, local anesthetics, and anabolic steroids were the most frequently detected. The author concluded that based on the evidence presented, deliberate “doping” in Great Britain was relatively rare (7). In the study presented here the number of positive reports issued to the authorities by year and race track in Illinois is presented in Table IV. The number of reported violations ranged from 123 (2006) to 40 two years later (2008). The increased intensity of testing and reporting most likely led to decreased doping and therefore a decreased number and percentage of positive results, and as a consequence, a decreased number of reports to the State Authorities. The most frequently identified drugs are listed in Table V. In addition to the findings detailed in Table V, one violation was reported for each of the following drugs: acetaminofen, buprenorphine, carprofen, chlorpromazine, codeine, desipramine, fluoxetine, glycopyrolate, guaifenesin, hydromorphone, imipramine, meperidine, mepivacaine, methamphetamine, nalbuphine, nalorphine, oxazepam, oxymorphone, phenobarbital, phentermine, prednisolone, prednisone, promazine, tramadol, and verapamil. As Table V clearly shows, the most frequent violations include the overages (concentrations of permitted medications equal to or exceeding the set threshold) of NSAIDs such as phenylbutazone with its metabolite oxyphenylbutazone (a total of 111) and flunixin (44 cases). Because both drugs are allowed Class 4 medications, there are thresholds established for phenylbutazone and flunixin (Table I), and therefore their concentrations in blood have to be monitored to differentiate acceptable therapeutic use versus administration for performance enhancing effects (8,9). The laboratory also found several other non-steroidal anti-inflammatory and analgesic drugs including diclofenac, indometacin, naproxen, ketorolac, acetaminophen, and carprofen, but with much lower frequency than phenylbutazone and flunixin. Over the five-year period of time (2004–2009), the number of reported violations with furosemide was high on the list (total of 25 violations) (Table V). Furosemide is a rapidly acting loop diuretic approved by the U.S. racing industry for treatment of exercise-induced pulmonary hemorrhage (EIPH)
Results and Discussion During the 5-year period of time (2004–2009), the laboratory analyzed a total of 91,808 specimens (45,210 urine samples and 46,598 blood samples) collected post-race from winning and special designation (horses other than those which took first place) Thoroughbred and harness horses, 302 perimortem and postmortem blood samples, and 116 special exhibits from 7 race tracks in the State of Illinois. The total number of specimens tested and the percentage of reported violations (confirmed presence of an unauthorized performance enhancing substance, or an overage of an authorized medication) in blood and in urine are presented in Table II. Table III presents the total number of special exhibits and perimortem and postmortem blood samples tested. The total number of violations reported was 413 (0.45% of the total number of specimens analyzed) including 207 drug-positive blood specimens (0.44% of all blood samples analyzed) and 206 urine samples (0.45% of all urine specimens analyzed). Two-hundred twenty violations were reported for harness horses and 193 for Thoroughbred horses. To date, there has only been a single report in the scientific literature known to the authors concerning the relative proportion of drug-positive samples to the total number of samples collected during the 12-year period between 1970 through 1981 in Great Britain including comparisons with
Table IV. Number of Positive Reports by Year and Race Track (2004–2009) Race Track Year
Arlington
Fairmount
Hawthorne
Balmoral
Maywood
DuQuoin
Springfield
Total
2005
2
9
22
36
30
1
0
100
2006
16
14
37
37
19
0
0
123
2007
13
6
17
24
11
2
0
73
2008
6
12
14
4
1
2
1
40
2009
6
5
8
28
29
0
1
77
Total
43
46
98
129
90
5
2
413
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(10,11). The use of furosemide is controversial and broadly and/or cerebral edema. It can also be applied to the skin to incriticized because of its potential to enhance the performance crease the cooling of body temperature. The threshold for of race horses (11). DMSO in urine established by the Illinois Racing Board is 500 During the same five-year period of time, the laboratory deug/mL (Table I). Ergonovine (ergometrine) is a potent ergot tected and reported 33 TCO2 violations with the total carbon derivative similar to LSD acting on alpha-adrenergic, dioxide post-race plasma concentrations ranging from 37 to 42 dopamine, and serotonin (5-HT2) receptors. The laboratory found a total of 21 cases positive for this drug after obtaining mmol/L. Typically the alkalinizing agent (e.g., sodium bicarinformation from harness track personnel of possible abuse. bonate) is administered to the horse by gavage to hypothetiThe laboratory was able to move quickly and add ergonovine to cally titrate lactic acid produced in muscles during the excesthe ELISA screening and develop a semi-quantitative GC–MS sive exercising, resulting in elevated TCO2 concentration in blood. In one study, it was determined that the stabled horses confirmatory procedure. The other groups of drugs detected in had a mean TCO2 level of 30 mmol/L (standard deviation 1.2) Illinois include antihistamines (pyrilamine, anti-asthmatic and the concentrations were normally distributed, whereas cromolyn), vasodilators (isoxsuprine, verapamil), muscle rethe pre-race TCO2 concentrations were not. The authors conlaxants (methocarbamol), tranquilizers (acepromazine, procluded that it is extremely unlikely for a normal horse to have mazine, chlorpromazine), local anesthetics (procaine, lidoa resting TCO2 concentration above 36 mmol/L (4). There are caine, mepivacaine), anticholinergic (glycopyrolate), and opioid few factors, such as the use of furosemide, sex, class and disanalgesics (morphine, tramadol, hydromorphone, nalbuphine, tance of race, and weather, that may be associated with the precodeine, buprenorphine, nalorphine, oxymorphone). In addirace TCO2 concentration in race horses (5,6). A broad review of tion, the laboratory previously reported two cases of etorphine “milkshaking” practices and its physiological and analytical (an extremely potent morphine analogue) administration to consequences was published by Kline (12). In TCO2 testing race horses (14). In a few cases, antidepressants (fluoxetine, scenario in Illinois, plasma samples are collected 90 min postimipramine, desipramine), benzodiazepines (oxazepam), glurace when all physiological post-exercise parameters come cocorticosteroids (prednisone, prednisolone), and even back to baseline. If the TCO2 concentration is elevated, a horse methamphetamine and phenobarbital were detected. is typically quarantined and TCO2 concentration monitored to rule out natuTable V. Drugs and Substances Most Frequently Reported (2004–2009) rally occurring high TCO2 plasma levels. Cocaine is classified as Class 1 drug acDrug Thoroughbred Harness Total cording to the ARCI Uniform Classification Guidelines for Foreign Substances Phenylbutazone and oxyphenylbutazone* 51 60 111 (1), and has a very high potential for imFlunixin 19 25 44 pacting the outcome of a race. During † 9 25 34 Cocaine (benzoylecgonine) the 5-year period of time (2004–2009), ‡ the laboratory detected benzoylecgonine 33 33 Total Carbon dioxide – (the primary inactive metabolite of coFurosemide 14 11 25 caine) in 34 urine specimens. In 2005, Ergonovine 0 21 21 the Illinois Racing Board issued new DMSO 6 15 21 medication rules establishing the § 1 12 13 Pyrilamine (O-desmethylpyrilamine) threshold level of 150 ng/mL for benCromolyn 5 4 9 zoylecgonine in equine urine (3). The ruling was associated with the possibility Diclofenac 3 6 9 of environmental contamination with coIndometacin 0 9 9 caine and the potential for exposure of Isoxsuprine 4 3 7 race horses to trace levels of the drug, Acepromazine [2-(1-hydroxyethyl) promazine]" 5 1 6 producing low levels of benzoylecgonine Methocarbamol 3 2 5 in horse urine. The issues of low benProcaine 0 5 5 zoylecgonine levels (below 150 ng/mL) in equine urine, their sources, and the conNaproxen 4 0 4 sequences and potential impact on a race, Ketorolac 0 3 3 were addressed by this group elsewhere Etorphine 2 0 2 (13). None of the benzoylecgonine levels 0 2 2 Lidocaine (3-hydroxylidocaine)# reported in this study exceeded 100 Morphine 2 0 2 ng/mL. The other most frequent violations in* Pharmacologically active metabolite of phenylbutazone. † Cocaine metabolite. clude DMSO and ergonovine (Table V). ‡ Thoroughbred horses are not tested for TCO . 2 DMSO is an organic solvent used in § Pyrilamine metabolite. " Acepromazine metabolite. horses as a liniment and for the treat# Lidocaine metabolite. ment of increased intracranial pressure
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Conclusions The number of reported violations of the total tested specimens in the State of Illinois was small, but a wide variety of performance-enhancing drugs and substances was shown. The most frequently reported violations include permitted therapeutic medications (phenylbutazone, flunixin). The authors conclude that those drugs having a valid medical indication and are commonly administered to horses also exhibit the greatest potential for being abused. Low levels of benzoylecgonine in horse urine most likely reflect a casual contact of a horse with cocaine-contaminated objects. The authors conclude that, based on the pharmacokinetics of cocaine in horses and a minimum effective cocaine dose capable of improving horse’s performance, the low levels detected in this study are not indicative of a deliberate doping. For many medications it would be difficult to conclude whether a drug was administered to a horse for the purpose of doping or the amount detected was residual. Finally, it is the authors’ conclusion that the most important steps in developing and maintaining a successful equine forensic toxicology program for the detection of doping with performance enhancing drugs are: communication with race track personnel, staying current on regional and global trends in doping and research and the ability to adjust one’s program to meet current needs.
Acknowledgment This work was funded by the Contract Number CC040631 from the Illinois Racing Board, Illinois Department of Revenue.
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2. C.R. Short, R.A. Sams, L.R. Soma, and T. Tobin. The regulation of drugs and medicines in horse racing in the United States. The Association of Racing Commissioners International Uniform Classification of Foreign Substances Guidelines. J. Vet. Pharmacol. Ther. 21(2): 145–153 (1998). 3. The General Assembly’s Illinois Administrative Code, Title 11: Alcohol, Horse Racing, and Lottery Subtitle b: Horse Racing Chapter I: Illinois Racing Board Subchapter C: Rules Applicable to all Occupation Licensees, Part 603 Medication, http://www.ilga.gov/commission/jcar/admincode/011/ 01100603sections.html (2011). 4. D.E. Auer, K.V. Skelton, S. Tay, and F.C. Baldock. Detection of bicarbonate administration (milkshake) in standardbred horses. Aust. Vet. J. 70(9): 336–340 (1993). 5. N.D. Cohen, S.D. Stanley, R.M. Arthur, and N. Wang. Factors influencing pre-race serum concentrations of total carbon dioxide in Thoroughbred horses racing in California. Equine Vet. J. 38(6): 543–548 (2006). 6. K. Kline, D. Fitzpatrick, L. Taddei, and A. Sukta. Effects of dose of furosemide on plasma TCO2 changes in Standardbred horses. J. Equine Vet. Sci. 26: 317–321 (2006). 7. M.S. Moss. Survey of positive results from racecourse antidoping samples received at Racecourse Security Services’ Laboratories. Equine Vet. J. 16(1): 39–42 (1984). 8. L.M. Neto, M.H. Andraus, and M.C. Salvadori. Determination of phenylbutazone and oxyphenylbutazone in plasma and urine samples of horses by high-performance liquid chromatography and gas chromatography–mass spectrometry. J. Chromatogr. B Biomed. Appl. 678: 211–218 (1996). 9. T.M. Dyke, R.A. Sams, and S.B. Cosgrove. Disposition of flunixin after intramuscular administration of flunixin meglumine to horses. J. Vet. Pharmacol. Ther. 20: 330–332 (1997). 10. K.W. Hinchcliff, P.S. Morley, and A.J. Guthrie. Efficacy of furosemide for prevention of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses. J. Am. Vet. Med. Assoc. 235(1): 76–82 (2009). 11. L.R. Soma and C.E. Uboh. Review of furosemide in horse racing: its effects and regulation. J. Vet. Pharmacol. Therap. 21: 228–240 (1998). 12. K.H. Kline. “Milkshakes” for the horse. J. Equine Vet. Sci. 24: 374–378 (2004). 13. C. Luckie, C. Whitney, M. Benoit, L. Taddei, A. Sukta, J. Peterson, D. Schwope, R.E. Gaensslen, and A. Negrusz. Detection and quantification of low levels of benzoylecgonine in equine urine. Forensic Sci. Int. 177: e21–e24 (2008). 14. J. Peterson, M. Benoit, C. Luckie, D. Schwope, A. Sukta, L. Taddei, C. Whitney, and A. Negrusz. A review of etorphine: a toxicological case study. Program and Abstracts, Society of Forensic Toxicologists Annual Meeting, Austin, Texas, S33, 2006.
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