The prevalence of a common metabolite of cocaine in the environment has created a need for the allowance of a minimum concentration of the substance in post-competition race testing, according to Fernanda Camargo, DVM, and Tom Tobin, DVM, PhD, DABT of the Gluck Equine Research Center at the University of Kentucky. Roberta Dwyer, DVM, MS, Dipl. ACVPM presented this study on Camargo’s behalf at the 2006 AAEP Convention.

According to Camargo and Tobin, exposing a horse to an amount of cocaine not uncommonly found on paper currency can result in a positive test, and 1mg of cocaine administered to a horse can produce about 100 ng/ml of Benzoylecgonine (BZE), a major urinary metabolite of cocaine.

The chances for exposure to this amount of cocaine are greater than one might imagine. According to Camargo and Tobin, one study stated that 79% of paper currency is contaminated with cocaine. (Other studies have estimated that contamination affects four out of five bills in circulation.)

“If you have a contaminated hand that touches the muzzle of a horse, puts the bit in the mouth, etc., the horse’s skin may readily absorb that cocaine,” Dwyer said.

Camargo and Tobin suggest that rather than a “zero tolerance” policy for BZE-positive horses, a cutoff value should be established, similar to the value allowed in human drug screening (the human workplace cutoff value for BZE is 300ng/ml for screening and 150 ng/ml for confirmatory tests).

“If trace amounts of BZE were not common in urine, then why would we have a human cutoff of 300 ng/ml, and things below that are considered negative?” Dwyer questioned.

Cocaine can be used as an equine stimulant, but doses ranging between 4mg/horse to 10mg/horse or more were required to produce any effect in previous research, Camargo and Tobin report. The ELISA test is extremely efficient in screening for BZE, and it can detect as little as 0.5ng/ml (1/2 a part per billion) of urine. The authors reported that when testing for cocaine metabolites was initiated in California, a number of horses tested positive for low concentrations of the metabolite.

Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse’s AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads