By: Sarah Carey
Veterinarians at the University of Florida College of Veterinary Medicine will be collaborating with the UF Racing Laboratory to investigate a local anesthetic with the potential for misuse in racehorses, thanks to funding from a national racing group.
The Racing Medication and Testing Consortium announced funding for two new tactical research projects, including UF’s, in February, following a meeting at Gulfstream Park in Hallandale, Florida. The projects were described as a continuation of the group’s ongoing focus on detecting and eliminating illicit substances in racing.
The drug UF researchers will be studying is an extended release form of bupivacaine, which is known to have longer-acting effects other local anesthetics more commonly used in equine medicine. Local anesthetics are often used to help localize the source of pain in equine lameness examinations, said Taralyn McCarrel, D.V.M., an equine surgeon and the grant’s principal investigator. An assistant professor of equine surgery at UF, McCarrel also directs the college’s pari-mutuel racing laboratory.
“Bupivacaine has been around for a while,” McCarrel said. “We don’t use it a lot, as most of the time we’re doing very short procedures and for those, we tend to use drugs that are shorter-acting. This is true also when we’re using them in a lameness examination; we only need the drugs to last a few hours in most cases.”
In an equine lameness examination, nerves in the lower limb are desensitized using local anesthetics. If the lameness improves, following the desensitization — often referred to as a nerve block — the source of the lameness is located within the area innervated by the “blocked” nerve.
Recently, two new liposomal formulations of bupivacaine were approved, one for use in humans and the other in dogs and cats. These formulations allow the drug to be slowly released over a number of days and were developed to control perioperative pain and reduce the need for opioid use, McCarrel said.
“In this new formulation, tiny droplets of bupivacaine are wrapped in a membrane, which is the liposomal component,” McCarrel said. “After injection, the liposomes start to break down, and gradually release these small pockets of drug over a long time.”
The investigators proposed this study because they were concerned for the potential that the new formulation could be used unethically to mask pain or an injury in a racehorse.
“Say you have a horse lame in its foot, and you can’t exercise it. You could potentially keep exercising or training the horse for up to three days, since it would be unable to feel its injury,” she said.
The UF researchers’ first goal will be to determine the minimal effective dose to block pain in a horse’s foot, and to assess how long that local anesthetic effect lasts. To do that, they will use horses that are part of a UF research herd that are trained over a period of time to achieve a racing level of fitness, using a treadmill housed at the college.
The researchers’ second goal is to better understand how the drug is metabolized and eliminated by the horse’s body.
To accomplish both goals, McCarrel will be working closely with Cynthia Cole, D.V.M., Ph.D., director of the UF Racing Laboratory, which oversees testing of racing animals statewide in collaboration with the state’s Division of Pari-Mutuel Wagering and is run through UF’s College of Medicine.
The Racing Laboratory’s role will be to determine the concentration of bupivacaine in blood and urine samples collected from horses in the study and to correlate those concentrations with the clinical effects observed in the study, she said.
“I’m excited, because this is a new chapter for the Racing Lab and the College of Veterinary Medicine working together,” Cole said. “Since the lab moved into the College of Medicine, we haven’t done as much collaborative research, but we’re hoping to do more.”
The Racing Medication and Testing Consortium is an accrediting body for horse racing testing facilities, including UF’s racing laboratory, in the United States. The organization has funded more than $2 million in drug testing research aimed at developing analytical methods for the detection of prohibited substances, or toward scientifically defensible withdrawal times and/or thresholds for therapeutic substances.