Less is More: Improving Equine Treatments

Friday, December 1, 2017

Mike Schoonover, DVM, MS, DACVS, DACVSMR, assistant professor of equine surgery at Oklahoma State’s Veterinary Medical Hospital, is always looking for ways to improve patient care. The equine section sees anywhere from 1,200 to 1,500 equine cases a year with the surgery service treating about 800 cases a year.

“Horses spend their whole life trying to kill themselves,” says Schoonover. “So we treat a lot of traumatic type injuries. We also treat a lot of sports medicine injuries such as western performance horses with injuries to the musculoskeletal system.”

One technique that Dr. Schoonover uses to treat injuries is intravenous regional limb perfusion.

“Intravenous regional limb perfusion is performed using a tourniquet to isolate the vasculature or the blood volume in the leg,” he explains. “We then inject a medication directly into a superficial blood vessel. Because of the tourniquet, the medication is contained within the leg for a period of time, usually around 30 minutes. This technique allows us to achieve high concentrations of a medication in a limb, using a smaller amount. The benefit is we use less medication so it’s less expensive. We also have the benefit of less systemic side effects because we’re using a smaller amount of medication and it’s more effective because the medication is really confined and concentrated in the area we want it.”

According to Schoonover, regional limb perfusion has been done for a number of years. However, the techniques vary widely among clinicians.

“Different clinicians use different techniques. Some might use a different time of tourniquet application or a different volume of fluid used to dilute the medication. So, the first study that we did looked at the effect of a given amount of amikacin, in antibiotic, added to different dilution volumes and how the different volumes affected the concentration of the medication in the different joints of the limb.  We used four different volumes ranging from 10 – 120 milliliters and measured the antibiotic concentrations in the knee or carpal joint and we also measured the concentration achieved in the foot or coffin joint.”

Schoonover and his team discovered that it didn’t really make a difference what volume of fluid was used to dilute the medication. The concentrations of the antibiotic achieved in the joints were very similar with all the dilution volumes. But what they did find led to a second study.

“What we found with the first study was that antibiotic concentrations achieved in the coffin joint were significantly higher than the concentrations in the carpal or knee joint. And actually the concentrations achieved in the knee were sub-therapeutic meaning they weren’t high enough to be effective in treating an infection in that location. So that led us to a second study where instead of using just a single tourniquet, which is placed above the knee, we placed two tourniquets—one above and one below. And that did show a significant difference. The second tourniquet allowed for higher concentrations in the knee and those concentrations were within the therapeutic range.

“What we determined from these two studies was if we are going to treat an infection in the foot, then using a single tourniquet is adequate. But if we are wanting to treat an infection in the knee or carpus, then a second tourniquet below the carpus is required in order to achieve appropriate antibiotic concentrations.”

Schoonover and his team also looked into using a common drug as an intravenous regional limb perfusion to treat navicular syndrome.

“Navicular syndrome is a progressive inflammatory degenerative problem that horses can develop in a very small bone of the foot. We see this disease a lot in middle aged quarter horses. I would say in the performance world upwards of 40 to 50 percent of those horses have some degree of pain related to navicular disease. It may not be performance limiting but if we did evaluations of all those horses, we would probably find some degree of disease.

“Bisphosphonates are drugs that have been used in human medicine for a number of years. They change the way bone is metabolized. The first drug licensed or approved for navicular syndrome in the bisphosphonate class is a drug called Tiludronate or Tildren®. It was originally approved in Europe and was used in the United States for a number of years under a conditional licensure. The label calls for administering the medication systemically or intravenously but there are some side effects such as transient colic and in some rare cases, horses developed renal failure. So there was a lot of thought about using this drug as a regional limb perfusion at a smaller dose in order to get the desired effect without the systemic side effects.”

Schoonover’s team decided to do a study to see if there was any efficacy in using Tiludronate as a regional limb perfusion.

“We recruited 12 horses that were diagnosed with navicular disease. Half of the horses were treated with the labeled systemic dose (1mg/kg) of tiludronate and half of the horses were treated with two regional limb perfusions, one into each foot, using a 0.1mg/kg dose. So the system group got a full dose and the regional limb horses got a total of 1/5 of the systemic dose (1/10 into each foot).

“We monitored those horses for lameness subjectively, by blinded observation, and objectively using the force plate for 200 days with monthly exams to determine their soundness. What we found was that the systemically treated horses did improve but the regional limb treated horses did not. That led us to a second study where instead of using just a single regional limb perfusion, we did multiple regional limb perfusions over a period of time. We decided to do three perfusions ten days apart.

Schoonover’s team recruited 15 horses for this study. Five horses received the same dose as the first study—a tenth of the dose or 0.1 mg/kg. Five horses received a 0.2 mg/kg dose or double that dose and then five horses had a saline placebo, which is just a control.

“We monitored these horses subjectively and objectively as before for 120 days and what we found was that neither dose really made a significant difference in soundness of these horses. It appears that using Tiludronate as a regional limb perfusion is not an effective treatment for navicular syndrome. We still recommend and do use Tiludronate systemically. Our hopes were that by using Tiludronate as a regional limb perfusion, we improve lameness and decrease some of the systemic side effects but our research indicates that that’s not the case.

“Regional limb perfusion is a very effective way to deliver any drug to the limbs or to the foot area. Rather than treat a horse with a large dose of a medication that may cause systemic problems, sometimes we can treat injury or disease locally. In many cases, intravenous regional limb perfusion is a more efficacious, less expensive and safer method of delivery compared to systemic treatment.”

Schoonover will continue to look for better ways to treat horses that come to OSU’s Veterinary Medical Hospital. As he completes each research study, the information will be published in veterinary medical journals so that others may benefit from his findings.

“A lot of our clinical studies are funded internally. Donations made to the OSU equine research program help fund a lot of these studies. So if someone is interested in helping out with our research endeavors, it would be greatly appreciated.”

If you would like to support equine veterinary medical research, please contact Chris Sitz, senior director of development with the Oklahoma State University Foundation at csitz@osugiving.com or 405-385-5170.