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14-02-2012 | Veterinary medicine | Article

Drug detection times for equine drugs published


The Pharmacokinetics of Equine Medication 2012 (PDF)

MedWire News: Australian scientists, working alongside the federal government, have published detailed information on the pharmacokinetics of 12 major equine medications.

Importantly, the report gives estimated elimination times, which the authors say will provide greater certainty for horse owners, trainers, and veterinarians.

"Because horses are prohibited from racing with any trace of drugs in their system, the administration of therapeutic drugs to horses in need of care has been a risky business," explained Martin Sillence (Queensland University of Technology, Brisbane), the report's lead author, in a press statement.

"It's been all too easy to unwittingly be caught out with a winning horse on race day, that's subsequently found to have traces of a drug in its system… The new schedule should change all this."

Sillence's team focused on 12 widely used equine medications: phenylbutazone, flunixin, ketoprofen, hydrocortisone, prednisolone, methylprednisolone, acepromazine, detomidine, buscopan, mepivacaine, lignocaine, and prilocaine.

Each compound was administered to at least 10 horses, and more than 20,000 plasma and urine samples were collected and analyzed.

For each compound, the authors calculated the time after administration at which plasma concentrations of the parent drug peak (Tmaxc) and the time after administration at which no drug or metabolite was detected in blood or urine in any horse (Ed).

Values for Tmaxc ranged from 3 minutes (detomidine) to 4.3 hours (phenylbutazone) while values for Ed ranged from 36 hours (hydrocortisone) to 10 weeks (methylprednisolone).

The Ed value does not represent the official detection time, say the authors, who then used a Bayesian probability model to investigate one drug, acepromazine, in depth. The model was able to account for variation between horses and also formed the basis of "a risk-based approach to judging an appropriate withholding time," say Sillence et al.

The researchers write: "This information should assist veterinarians to develop more effective treatment protocols for horses, and will assist the racing industry regulators in setting appropriate detection times and reporting levels for therapeutic substances in animals that compete."

They add: "Finally, as the information will be available to racing jurisdictions worldwide, this will assist Asian, European and American authorities in avoiding duplication of effort and moving towards a harmonised approach to drug detection."

By Joanna Lyford