Recommended withdrawal guidelines for detomidine, commercially known as Dormosedan, may face review after a recent study suggested horses could test positive while adhering to the withdrawal guidelines, depending on the dose they receive. The current guideline from the Racing Medication Testing Consortium suggests the threshold for a positive be set at 2ng/ml in urine and 1 ngl/ml in blood, with the recommended withdrawal for a 5 mg intravenous dose set at 48 hours.
Detomidine is a relatively short-acting sedative with some analgesic properties and may be used to reduce stress during medical procedures or travel, or in hospital settings.
Recently, the Kentucky Equine Drug Research Council funded a study to examine the behavior of a 20 mg dose (given intravenously or intramuscularly), which some veterinarians say is also used in the field, depending upon the situation.
For tests of the drug using a blood sample, a 20 mg dose was well below the recommended threshold by 48 hours post-administration; in some cases the drug was almost undetectable. In the case of urine tests for detomidine however, several samples were over the threshold at 48 hours.
Unfortunately, the study was designed to stop at 48 hours post-administration, and therefore did not shed light on whether extending the window to 72 hours would be sufficient to avoid accidental positive tests.
“The dose that was investigated initially was a 5 mg dose. A lot of our veterinarians use a 5 mg dose. Dr. [Andy] Roberts and some other veterinarians wanted to know if they could use a 20 mg dose. It's going to give a bigger effect,” he said. “Very few of these substances that affect the central nervous system have a dose that's fixed. It's a dose range, and I think it's a legitimate question on Dr. Roberts' part about using that 20 mg dose.”
Sams, who is a member of the RMTC's Scientific Advisory Committee, said these types of revisions are to be expected as more information comes to light about different drugs and their behavior in horses. Unfortunately, there is a disparity between the public's thirst for uniform regulations and the amount of time (and money) it takes to complete studies like this one, which ultimately highlights the need for more research.
“The process was moving very slowly years ago and the RMTC came under enormous pressure to move forward and have thresholds for all of these substances that veterinarians had identified. The future of the RMTC, I think, was on the line at that point,” Sams remembered. “We made some less-than-optimal choices with regard to doses, but veterinarians were involved in every step of the way.”
Editor's Note: Dr. Mary Scollay, member of the RMTC Scientific Advisory Committee and the EDRC, pointed out this finding does not invalidate the current withdrawal guideline for the 5 mg dose; rather, it shows horses may test positive if receiving a 20 mg dose at the 5 mg withdrawal time.
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