Illicit Drugs in Horses: BenZoylEcgonine Thresholds in Urine

In 1985, the Kentucky Racing Commission directed the Equine Pharmacology program at the University of Kentucky to work on improving testing for performance-enhancing drugs. The outcome was the introduction of Enzyme-Linked-ImmunoSorbant Assay (ELISA) testing into racing. ELISA tests are exceptionally sensitive, detecting drug/drug metabolites at low parts per billion (nanograms/ml, equivalent to one second in 32 years) or high parts per trillion (picograms/ml, or one second in 32,000 years) concentrations. This high sensitivity is essential for the detection of illicit drug use in horses. However, the regulatory authorities very soon ran into the problem of these tests detecting minuscule traces of BenZoylEcgonine [BZE] in horse urine.

This is a problem because BZE is the major urinary metabolite of cocaine, which is very efficiently excreted in horse urine. Exposure to 1 mg of cocaine can yield 100 ng/ml (100 ppb) of BZE in horse urine. Since a BZE ELISA can detect 1 ng/ml or less of BZE, these tests can theoretically detect exposure of a horse to one hundredth of a milligram of cocaine.

To put this into perspective, about 300 metric tons of cocaine are imported into the United States each year, and paper currency is “highly” contaminated with cocaine. In one study on 136 one-dollar bills, 79% carried detectable cocaine, 50% carried microgram amounts, and one bill carried 1.3 mg. If 1.3 mg were given to a horse, it could easily yield a 100 ng/ml detection, which is far below that required to influence racing performance.

Reviewing these matters, Dr. C. Kolias-Baker (2002) noted that 2.5 mg of cocaine, an amount sufficient to yield detectable urinary concentrations of BZE for 24 hours, “could easily be transferred from a cocaine abuser’s hands to the mouth or muzzle of a horse” and yield concentrations similar to those “that are occasionally found in urine samples collected from show and race horses.” Similarly, Dr. Scott Waterman of the Racing Medication and Testing Consortium noted that “the presence of cocaine in a horse’s blood or urine is not a sure sign that somebody is trying to fix a race, because trace amounts of cocaine could be spread by casual contact with human users” (C. Wilson, The Associated Press. 12/8/2005).

When sensitive BZE tests were introduced in California, the outcome was dramatic, and within weeks a number of California trainers, some very prominent, were associated with “trace” BZE identifications. When the dust settled, a number of important administrative changes had occurred.

The first change in California was the creation of an equine medical director position to oversee drug testing and other procedures. The second change was the introduction of thresholds, or cut-offs, for certain environmental substances in racing horses. These changes follow well-established precedents in human medicine. The equine medical director position is equivalent to a human medical review officer, and it is structured to address situations such as the multiple BZE “identifications” in California racing in the late 1980s.

The introduction of urinary cut-offs for BZE were modeled on the 150 ng/ml BZE cut-off present in human workplace drug testing. In 1999, Ohio introduced a BZE cut-off of 150 ng/ml. This threshold has since been adopted in Louisiana, Illinois, and Oklahoma, and lower cut-offs for BZE are in place in Washington state and Florida. And most recently, recognizing the regulatory implications of this problem, the U.S. Racing Medication and Testing Consortium has created an environmental contaminants subcommittee to evaluate and recommend approaches to this problem. It is chaired by Kent Stirling, executive director of the Florida Horsemen’s Benevolent and Protective Association.