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Equine drug testing

Racehorse drug testing began in the early 1900s. It is the longest established, broadest in scope, and possibly the most sensitive drug testing program in existence. Racehorse drug testing is performed within an extremely stringent regulatory context. This testing has shown that the incidence of deliberate use of performance affecting substances in horse racing is extremely small.

Before the mid-1980s, the use of high potency performance altering substances in racing was less well controlled due to the inadequacy of analytical technology. Around that time, highly sensitive ELISA testing of horse urine was introduced to racing regulators by a group at the University of Kentucky. This proprietary technology essentially solved the problem of the abuse of high potency drugs in racing horses. ELISA tests are now marketed worldwide out of Lexington, Kentucky.

The ease with which traces of therapeutic medications and dietary and environmental substances can be detected using current testing technology is leading scientists and regulators away from the "zero tolerance" approach to drug testing, which many authorities now see as outdated. Increasingly common today is the use of regulatory limits or "thresholds" (the urine or blood concentration of a substance below which there is no pharmacological activity, i.e., there is no effect, a so called "No Effect Threshold" or NET).

Recent challenges in drug testing include the development of effective regulatory methods for the newer hormonal products such as the various human recombinant erythropoietin products and variants and growth hormones. In 2006 a high-quality ELISA test for human recombinant erythropoietin became available, and racing chemistry has scored a major scientific breakthrough by developing the first Mass Spectral Confirmation method to detect use of human recombinant erythropoietin (rhEPO) in horses or any species.


Background and definitions

There are at least 10 million known chemical substances and more than 4,000 prescription medications. Racing regulators in the United States divide drugs and medications into two major groups.

Performance-enhancing substances
Identification of these substances in a horse is viewed with great regulatory concern. Testing for these substances usually proceeds at the highest level of sensitivity possible, so-called "zero-tolerance" testing. About 850 or so substances are classified by the Association of Racing Commissioners International (ARCI) Uniform Classification System for Foreign Substances as potentially performance enhancing in a five class system. The most complete listing of such substances is found at http://www.arci.com/druglisting.pdf.

Therapeutic medications
There are more than fifty of these agents used therapeutically in horses in training. Since about 2000, it has come to be more generally accepted that "limitations" on testing for therapeutic medications are necessary. These limitations are variously called "thresholds" or "reporting levels," or "decision levels" (California) depending on the semantic preference of individual jurisdictions. These terms apply to the blood concentration of a medication below which the substance has insignificant pharmacologic affect.

Performance-modifying substances

Among the equine stimulants are amphetamines, as well as the amphetamine-like drugs such as methylphenidate (Ritalin).

Horses can also be medicated to win by relaxing them, and allowing the horse to run its best possible race. The widely used tranquilizer acepromazine, and any number of related or equivalent agents, have been used in this way. Of course, higher doses of tranquilizers can also decrease a horse's performance.

Improving a horse's "wind" by opening its airways through the use of bronchodilators may also improve performance, especially in an animal that is sub-clinically broncho-constricted. Some bronchodilators can also have a stimulant effect.

Behaviorial modifiers
Veterinarians certify horses as being sound in "wind and limb." Obviously, medications that can affect these parameters and also the "attitude" or "behavior" of a horse have the potential to affect both the presentation of a horse and also, presumably, the outcome of a race.


The Introduction of ELISA testing (1988)
In the mid-1980s, equine drug testing was for all practical purposes dependent on a screening technique called thin layer chromatography (TLC). This technology is not particularly sensitive, and in the mid-1980s some horsemen were reportedly attempting to affect the outcome of horse races by using high potency narcotics, stimulants, bronchodilators, and tranquilizers with impunity. In 1988 ELISA testing was introduced to racing by a group at the University of Kentucky. It soon became the primary technique employed in equine drug testing. ELISA is an acronym for Enyme Linked Immuno Sorbent Assay. Simply put, an ELISA test is a variant on the home pregnancy test technology. It requires a drop of urine, can be performed relatively rapidly, is highly sensitive, and test results can be read by eye. Initially, the ELISA tests were "one-step" tests meaning that urine was added to the test well followed by the addition of antibody for the test. This was expensive as much more antibody was wasted than reacted on the test. Later, a cheaper "two-step" method was devised. Currently, at least one company in the US primarily deals in "one-step" tests, whil the other rwo in the US deal in "two-step" tests.

Confirmatory Testing
While ELISA screening or testing is fast and fairly sensitive, it is far from specific. The second and absolutely critical step in the drug testing process is confirmation of positive ELISA tests using more sophisticated techniques such gas or liquid chromatography combined with mass spectrometry (GC/MS, LC/MS, or LC/MS/MS). Mass spectrometry is the gold standard drug identification. It is also extremely sensitive. Some drug testing laboratories have moved toward using the more specific mass spectrometric techniques as their primary screening and testing technique.

Zero Tolerance Testing
Zero tolerance testing is not testing down to "zero" molecules, which no chemist can accomplish, but rather testing to the limit of detection (LOD) of the best available technology. In other words, "zero tolerance" refers to the racing regulators' philosophy in regulating drug use in race horses—even trace amounts of drugs are not tolerated. While detecting trace amounts may be an entirely appropriate approach for performance altering substances which have no approved veterinary use, it is not considered appropriate for therapeutic medications which may be present in trace amounts having negligible or no pharmacological activity. Therapeutic medications are approved substances used to maintain the health and welfare of horses.

Thresholds, including “no effect thresholds” (NETs)
The equine blood concentration of a medication below which pharmacologic activity is insignificant.

Withdrawal time
The length of time after the administration of a medication required for the metabolism and elimination of the medication. After this time the medication no longer present or has insufficient concentration to produce a pharmacologic effect.

Further information


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