Laminitis

An Evidence- Based Look at Multimodal Laminitis Treatments

By Paul Basilio

It would be a bit of an understatement to say that pain management in the laminitic horse is challenging. Between the types of pain and the dearth of evidence on the multitude of treatment options, clinicians often find themselves in the weeds.

In addition to therapeutic shoeing and hoof support, multimodal treatment typically gives a patient their best shot at recovery. But which ones to try? And what about the evidence?

To help firm up the veterinarian’s armamentarium, Katherine Ellis, DVM, a clinician in equine sports medicine rehabilitation at the University of Georgia, recently described several pharmaceutical and non-pharmaceutical modalities in a virtual presentation at the 66th AAEP Annual Convention.

CASE #1: Too Much of a Good Thing

Dr. Ellis described a 14-year-old Quarter Horse gelding that managed to make his way into the feed room and ate half of a bag of sweet feed within 24 hours. The horse had an acute AAEP grade 4 lameness in both forelimbs and moderately increased digital pulses.

“For this horse, you might consider an NSAID, digital hypothermia and vasodilators, such as pentoxifylline and acepromazine, which do not have direct analgesic effects,” she said.

Anecdotally, many clinicians regard phenylbutazone as the most efficacious and consistent nonsteroidal anti-inflammatory (NSAID), but several studies offer alternatives. “Although they may not have evaluated laminitic horses, other studies have shown that other NSAIDs may be as effective as phenylbutazone,” Dr. Ellis said.

Doucet, et al, for example, showed that firocoxib at 0.1 mg/kg every 24 hours was as effective as phenylbutazone at 4.4 mg/kg orally every 24 hours for horses with osteoarthritis. A 2005 study looking at navicular syndrome showed that flunixin meglumine 1.1 mg/kg IV was as effective as phenylbutazone 4.4 mg/kg orally.

“If laminitic pain is not controlled with one NSAID, it might be worthwhile to try a different one,” she added, “although evidence in the laminitic horse is lacking.”

A 1995 study involving horses with naturally occurring, bilateral laminitis showed that ketoprofen at 3.63 mg/kg was more effective at controlling pain than phenylbutazone at 4.4 mg/kg.

One modality that does have the backing of a breadth-of-controlled research studies is icing. Continuous digital hypothermia performed just below the carpus using an ice boot or an ice bath can significantly reduce lamellar injury.

Vasodilators such as pentoxifylline have no direct analgesic effects, but they are thought to have indirect effects by helping to restore normal blood flow to the foot. But is there evidence for use in equine laminitis? “

Unfortunately not,” Dr. Ellis said.

Some things are known, such as pentoxifylline’s extremely variable absorption in the horse after oral administration. Another study found that pentoxifylline at 4.4 mg/kg orally every 8 hours for 10 days did not increase blood flow in the digit of healthy horses. It has also not been evaluated in the laminitic horse.

Another drug that has no direct analgesic effect is acepromazine, a phenothiazine tranquilizer.

“We do have studies that show increased blood flow and arterial diameter in the dorsal metatarsal artery in horses,” she explained. “In addition, IV administration at 0.06 mg/kg has been shown to increase digital and laminar blood flow in normal horses.”

These studies have shown an increase in digital blood flow in healthy horses, but it is unknown if the increase occurs in laminitic horses as well.

CASE #2: Chronic Laminitis in the Field

A 25-year-old Paint gelding with a prior history of pituitary pars intermedia dysfunction (PPID) has chronic laminitis, predominantly affecting the front feet. Previous episodes have typically improved after a few days of phenylbutazone, but the current episode has lasted for 2 weeks with no improvement. His appetite has also been decreased, and central sensitization is suspected.

“You might consider continuing to use an NSAID given the horse’s pain level, but I would consider switching to firocoxib, given the decreased appetite and chronic use of phenylbutazone,” Dr. Ellis said. “Since we have evidence of central sensitization, we could also try gabapentin and some non-traditional treatments, such as transcutaneous electrical nerve stimulation [TENS], acupuncture, and manual therapy.”

Gabapentin has shown mixed results in horses. One study evaluated gabapentin at either 5 mg/kg or 10 mg/ kg orally 3 times daily for 14 days in horses with chronic osteoarthritis. No significant improvement in lameness was seen with either dose.

“There have been some individual case reports in horses with chronic laminitis that showed improvement with gabapentin.” Dr. Ellis added. “It has a low bioavailability when administered orally, so higher doses are likely needed to be effective.”

Unfortunately, there is no evidence in horses— laminitis or not—regarding TENS therapy. “All of our evidence comes from human medicine, which does show some conflicting results,” she explained. “However, many studies have shown improved pain control for both postoperative pain and chronic pain.”

Acupuncture, however, has been studied more in horses. One study showed that 2 acupuncture treatments performed 1 week apart improved lameness scores in horses with chronic laminitis. Another study showed improvements in subjective pain levels in 6 of 7 horses with chronic laminitis.

For secondary pain of the axial skeleton, manual therapy, such as massage, chiropractic and physiotherapies, can also be considered.

“While evidence for pharmaceutical and non-pharmaceutical approaches in the laminate course are somewhat limited,” Dr. Ellis concluded, “We do have multiple treatment options available.”

For more information:

Owens JG, et al. Effects of ketoprofen and phenylbutazone on chronic hoof pain and lameness in the horse. Equine Vet J 1995;27:296-300.

Doucet MY, et al. Comparison of efficacy and safety of paste formulations of firocoxib and phenylbutazone in horses with naturally occurring osteoarthritis. J Am Vet Med Assoc 2008;232:91-97.

Erker RS, et al. Use of force plate analysis to compare the analgesic effects of intravenous administration of phenylbutazone and flunixin meglumine in horses with navicular syndrome. Am J Vet Res 2005;66:284-288.

Liska DA, et al. Pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite after oral and intravenous administration of pentoxifylline to healthy adult horses. Am J Vet Res 2006;67:1621-1627.

Ingle-Fehr JE and Baxter GM. The effect of oral isoxsuprine and pentoxifylline on digital laminar blood flow in healthy horses. Vet Surg 1999;28:154-160.

Hunt RJ, et al. Effects of acetylpromazine, xylazine, and vertical load on digital arterial blood flow in horses. Am J Vet Res 1994;55:375-378.

Caldwell FJ, et al. Effect of PO administered gabapentin on chronic lameness in horses. J Equine Vet Sci 2015;35:536-540.

Faramarzi B, et al. Response to acupuncture treatment in horses with chronic laminitis. Can Vet J 58(8):823-827.