Kentucky Rescinds Dextrorphan Positives, But No Victory For Proponents Of Environmental Contamination

by | 02.23.2017 | 4:24pm

The Kentucky Horse Racing Commission agreed earlier this year to rescind three recent violations related to overages of dextrorphan, a metabolite of dextromethorphan. However, according to Dr. Mary Scollay, equine medical director for the commission, the dismissal shouldn't be seen as a victory by horsemen and veterinarians concerned about environmental contamination.

The three findings were detected in November 2015, January 2016, and April 2016. Dr. Richard Sams, laboratory director at LGC Sport Science Lab, discovered a newly-published academic research paper in late 2016 designed to study genetic differences in rates of drug metabolism in horses. One of the substances examined was dextromethorphan, and the information shed new light on the rate at which the drug breaks down in the horse's body.

Dextrorphan is the substance that appears as a result of dextromethorphan breaking down. Dextromethorphan is a common ingredient in human cough syrups, although it can also be a drug of abuse in humans in high concentrations, and acts as an anesthetic and causes hallucinations. There is no FDA-approved use for dextromethorphan in horses, but the commission has received information it has been used experimentally to stop nervous behaviors such as cribbing. Dextromethorphan is a Class B substance according to ARCI model rules, and per Kentucky regulations.

The new study indicated that as dextromethorphan disappears from a horse's system, dextrorphan concentrations briefly increase before tapering off more gradually than previously realized. Investigators could not know when the drug was administered in the Kentucky cases or at what dose. The study did shed light on the timeline for the drug's metabolism at the therapeutic dose of 2 mg/kg, however; if the drug was given intentionally at that dose, it had to have been introduced 48 to 72 hours pre-race. At that timeline, the commission decided the drug's administration was “irrelevant” to the horses' performance.

“These cases were not rescinded because of a determination of environmental contamination,” said Scollay. “You likely have seen that in some of the trade press, and that was a conclusion made by someone who was not party to the discussion. To this point, dose, route, and time of exposure remain unknown. There is no evidence that dextromethorphan was present in any of the horse's environments, nor that if it were present, it could have resulted in an exposure that could have caused a positive test.”

Environmental contamination has received increasing attention at regulatory conventions and in the press recently as some veterinarians and horsemen have voiced concerns that laboratory levels of detection for medication in post-race tests have grown too strict. Some research has indicated certain drugs can linger in hay or bedding for longer than others, and trainers say they worry they could incur a positive drug test from a testing barn stall or from a groom touching a horse's nose or mouth with residue from an over-the-counter medication on their hands. Scollay is skeptical of such claims, but said Tuesday she believes a positive acquired from a handler in this case would constitute “poor medication control” — still the responsibility of the trainer, as absolute insurer of the animal.

“If somebody had dextromethorphan on their hands, and they put their hands in a horse's mouth, I'm not buying that's environmental contamination, that's sloppy management,” said Scollay. “I think you just saw the commission acted very reasonably after getting more information.”

Additionally, Scollay pointed out if it were really so easy to cause an inadvertent positive from a handler, she would expect to see more overages of common substances like caffeine and nicotine, which Kentucky's laboratory does test for but has never found in a horse. The state has also never had findings for codeine or acetaminophen both active ingredients in commonly-prescribed painkillers for people.
The Racing Medication and Testing Consortium provides trainers with a brochure suggesting best practices for avoiding unintended positive tests. That document is available here.

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