University of Florida veterinarians to study bupivacaine in racehorses

Horses racing at Churchill Downs Racetrack in Louisville, Kentucky, home of the legendary Kentucky Derby. Veterinarians at the University of Florida College of Veterinary Medicine will be investigating a local anesthetic with the potential for misuse in racehorses, thanks to funding from a national racing group, according to a release from the university.

The Racing Medication and Testing Consortium announced funding for the project in February, which it says is in line with its focus on eliminating illicit substances in racing, the release states.

UF researchers will be studying an extended-release form of bupivacaine, which has longer-acting effects than other local anesthetics commonly used in equine medicine. These agents are often used to help localize the source of pain in equine lameness examinations, says Taralyn McCarrel, DVM, an equine surgeon, an assistant surgery professor and the grant's principal investigator.

“Bupivacaine has been around for a while,” Dr. McCarrel says in the release. “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 an equine lameness examination, nerves in the lower limb are desensitized using local anesthetics. If the lameness improves, the source of the lameness is known to be in the area innervated by the “blocked” nerve.

Recently, two new liposomal formulations of bupivacaine have been approved, one for use in dogs and cats (Nocita-Aratana) and the other for humans. These formulations allow the drug to be released slowly 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,” Dr. McCarrel says. “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 about 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 says.

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. These horses 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, Dr. McCarrel will be working closely with Cynthia Cole, DVM, PhD, 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, Dr. Cole says in the release.

“I'm excited, because this is a new chapter for the Racing Lab and the College of Veterinary Medicine working together,” Dr. Cole says. “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.