Learn what veterinarians are doing to improve how they control equine pain
As a veterinarian and writer, I’ve studied and written a lot about analgesics over the years, but the true value of these pain management drugs recently hit a little too close to home. At the beginning of 2016, my son sustained a spiral fracture of his right femur (thighbone), requiring two surgeries, four months in a wheelchair, and close to 50 hours of painful physical therapy. Thankfully, his doctors prescribed various medications to help control his discomfort—beginning with intranasal fentanyl right there on the football field, followed by other opioids, non-steroidal anti-inflammatory drugs, and nerve blocks at the hospital, to name a few.
My son was lucky. Years ago, patients would have to endure excruciating pain throughout their recovery (remember Little House on the Prairie or Dr. Quinn Medicine Woman?). The same applies to horses. Author James Herriot once described helping a horse suffering from the severe pain of acute laminitis following grain overload by standing with him in a near-frozen babbling brook for hours on end.
“Few other options were available in those days,” says Chris Sanchez, DVM, PhD, Dipl. ACVIM, an assistant professor in the Department of Large Animal Clinical Sciences at the University of Florida’s College of Veterinary Medicine, in Gainesville. “Now, equine veterinarians have a variety of safe, effective, and mostly economical analgesics at the ready, with several more in various stages of testing.”
A complete description of what drug(s) to use in which situation and at what dose and frequency is beyond the scope of this article, but we’ll briefly review the tried-and-true analgesics before delving into some of the more novel pharmaceutical agents and alternative modalities introduced over the past few years. Wherever possible, we’ve provided study references to guide readers to salient data and additional information.
An Eye for an Eye
The classic take on this phrase is to exact punishment commensurate with a crime: eye for eye, tooth for tooth, foot for foot, etc. until the criminal apparently either learns his or her lesson or runs out of body parts. If pain is the enemy, then perhaps we should embrace this sentiment, showing pain that we will fight back with a vengeance.
Our current armamentarium for fighting pain relies heavily on the following “big three”:
- Non-steroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone (Bute) and flunixin meglumine (Banamine);
- Opioids such as butorphanol, morphine, and tramadol; and
- Xylazine and other α2-adrenergic agents used for sedation, anesthesia, muscle relaxation, and analgesia.
Although these types of drugs have been around for a while, they remain widely accepted as effective go-to medications for a vast array of acute and chronic conditions, including:
- Lameness and musculoskeletal disorders, predominantly osteoarthritis (OA) and laminitis;
- Lacerations and other injuries;
- Corneal ulcers and other ophthalmic conditions; and
- Reproductive emergencies such as dystocia (difficult birth), metritis (inflammation of the uterus), and mastitis (mammary gland inflammation).
That said, if you’ve ever experienced a substantial level of discomfort, you know these medications aren’t always enough when administered individually, tend to wear off quickly, or only come in oral form (which takes longer to kick in because the medication must be absorbed from the gastrointestinal tract before reaching the bloodstream). Researchers have come up with alternative therapies to improve how they manage human patients, so it’s logical that equine veterinarians would mirror those advances with their four-legged patients.
A New Generation of Pain Meds
“From borrowing some medications and pain control strategies from human medicine, substantial advances have occurred and continue to provide better control over a variety of types of pain in horses of all ages and breeds,” says Lori Bidwell, DVM, Dipl. ACVAA, a boarded veterinary anesthesiologist and certified veterinary acupuncturist and co-owner of East-West Equine Sports Medicine in Kentucky.
For example, three newer NSAIDs have recently been explored in horses: firocoxib (Equioxx), topical 1% diclofenac sodium cream (Surpass), and meloxicam.
Firocoxib is a COX-2 inhibitor. This product is FDA-approved for use in horses with OA, but manufacturer instructions state that it can only be administered for 14 consecutive days (for safety reasons and to avoid adverse reactions associated with NSAIDs). Bidwell says one exciting advance in analgesia is that Equioxx is now available as a 57-mg tablet labeled specifically for horses.
“The 57-mg Previcox tablets (labeled for dogs) have been used off-label in horses for several years with success for chronic pain management and performance–related pain,” says Bidwell.
Veterinarians can also prescribe topical 1% diclofenac sodium cream for arthritic horses. Researchers continue to find more uses for diclofenac, recently identifying diclofenac epolamine (rather than sodium) as more capable of deeply penetrating skin than the sodium version.1
Meloxicam also appears promising for managing postoperative pain and inflammation after musculoskeletal and soft-tissue surgeries. In 2015 a group of Canadian veterinary researchers reported that human meloxicam tablets (15 mg) “behaved” similarly (i.e., how the drug is dispersed and metabolized throughout the body) to the equine liquid formulation (15 mg/mL) approved for use in horses in Europe when administered at an average dose of 0.6 mg/kg body weight. “Use of human meloxicam tablets compounded with molasses would be expected to produce a similar clinical response in horses as the approved oral product from the European Union,” they concluded.2
Another team, from Germany, subsequently found that a single intravenous dose of meloxicam, followed by once daily oral administration for four consecutive days, provided appropriate pain relief for horses undergoing partial splint bone fracture removal.3
As for the drug’s ability to combat colic pain, authors of a 2014 study assure us that meloxicam is as effective as flunixin meglumine for controlling the torturous pain experienced by horses suffering naturally occurring strangulating small intestine lesions.4
“Meloxicam is especially beneficial in foals,” says Rachel Hector, DVM, an anesthesiology resident at Colorado State University (CSU) Veterinary Teaching Hospital, in Fort Collins. “This is because traditional NSAIDs have prolonged clearance rates in foals, while meloxicam is cleared more rapidly, which may confer a benefit in foals where it is used for long treatments.”
In addition to NSAIDs, the local anesthetic lidocaine remains a common choice among equine veterinarians managing painful conditions. Intravenous (IV) use of lidocaine is common during colic surgeries and can also be useful in the field when treating horses with laminitis. Veterinarians also use IV ketamine and dimethyl sulfoxide to treat pain and inflammation, respectively.
Lesser-known options for managing pain in horses are tramadol and gabapentin. Tramadol is an opioidlike medication that physicians and small-animal veterinarians have applied extensively. Recently, equine veterinarians have explored the merits of using IV tramadol in foals and mature horses. In 2016 alone, several research groups scrutinized tramadol, either alone or in combination with other pain-relieving agents, with positive results. However, other papers show that tramadol has no analgesic effects in research models in horses; higher doses only increase excitatory side effects; and injectable formulations are expensive.
Bidwell says tramadol is not yet a practical option for horses. Hector adds that “tramadol may have a role as a part of a multimodal analgesic plan, but is not likely to be effective when used on its own.”
Not to be outdone is the “nerve pain” medication gabapentin. It reportedly attacks pain from a different direction than tramadol, lidocaine, and the “big three.” Horses with chronic conditions—such as laminitis—seem to benefit from having this drug added to the mix.
“Gabapentin works by quieting excitable nerves and allowing other pain medications to be more effective,” says Bidwell.
“Similarly to tramadol, there is very little peer-reviewed evidence on gabapentin,” says Hector. “Like human doctors, veterinarians are challenged by the need to find an appropriate dose and regimen; however, as a part of a multimodal approach there is good anecdotal evidence of efficacy and very limited side effects.”
Despite these and other options, veterinarians agree that our cup of pain meds still does not runneth over, which creates opportunities for those interested in exploring other options.
Although many discussions surrounding pain frequently focus on the acute (short-lasting) type, there are still scores of horses suffering from low-grade chronic aches and pains. Managing the horse that’s sore or “off” is as important, and potentially as challenging, as treating a thrashing, colicky horse. Enter complementary and alternative veterinary medicine (CAVM).
This is not synonymous with, “Hey, I tried everything else, so might as well.” In fact, there is a substantial body of data supporting these therapies in both human and veterinary medicine.
Bidwell says, “Five thousand years of evidence, plus a large amount of research within the last 10 years, support the use of alternative therapies, including acupuncture. Analgesia due to the release of systemic endorphins or opioids through acupuncture has anti-inflammatory effects and causes muscle relaxation.”
Another technique, medical massage, involves manually manipulating tight muscles or trigger points until they relax without the use of pharmaceutical drugs.
Other alternative options include the homeopathic medications traumeel and Zeel. Traumeel and Zeel both contain combinations of small amounts of Arnica and Rhus toxicodendron, which can all help relieve pain, inflammation, and stiffness associated with muscles and joints, says Bidwell. Both products are permitted for use in horses participating in international competition.
Even oral joint health supplements can have anti-inflammatory effects. Study results show that glucosamine, chondroitin sulfate, avocado-soybean unsaponifiables, and green tea extracts (epigallocatechin gallate) reduce inflammation in equine cartilage cells in lab studies.
In a 2014 review article titled “Pain control in horses: What do we really know?” Sanchez and colleagues succinctly summarized the challenges with diagnosing pain.
“Recognition of overt pain behaviors, such as rolling, kicking at the abdomen, flank watching, lameness, or blepharospasm (squinting), may be obvious,” they wrote. “Subtle signs of pain can include changes in facial expression or head position, location in the stall, and response to palpation or human interaction.”
“As prey animals, horses are often adept at hiding signs of pain until it becomes so severe that they can no longer mask it … at the eleventh hour, so to speak,” says Hector.
Detailed pain scales allow owners and veterinarians to recognize more subtle signs of pain sooner and help caregivers assess treatment efficacy objectively.
Colorado State University is renowned for its canine and feline pain-management scales. Developed in the mid-2000s, these scales guide veterinary professionals in identifying discomfort using behavioral and physiological parameters. You can spot such scales posted in veterinary hospitals throughout the world.
Researchers at CSU developed a similar scale for horses around the same time. The equine pain scale (available at http://csu-cvmbs.colostate.edu/Documents/anesthesia-pain-management-pain-score-equine.pdf) includes behavioral cues, such as head and ear position and restlessness, along with clinical parameters, such as heart rate, eye position, response to palpation, and degree of lameness.
Although veterinarians designed the pain scale for identifying acute pain typically observed in surgical patients, the descriptors used can be applied to any horse in discomfort, including those with OA or equine asthma syndrome.
Other pain scales for horses also exist. In 2016 Dutch researchers published the Equine Utrecht University Scale for Composite Pain Assessment (EQUUS-COMPASS) and Facial Assessment of Pain (EQUUS-FAP). They tested these scales’ efficacy for recognizing pain in horses with acute colic, as well as a healthy control population of horses, and found that both EQUUS-COMPASS (using behavioral and interactive parameters) and FAP were valid methods of identifying painful, colicky horses. Moreover, pain scores using both scales differed significantly between horses with colic that could be treated conservatively versus those requiring surgery or euthanasia.
Similarly, researchers from the University of Milan recently tested their Horse Grimace Scale (HGS) on horses with acute laminitis. They suggest that the HGS requires further validation, but the facial-expression-based pain coding system appears to be an effective means of assessing pain in acutely laminitic horses and does not require the horse to walk or trot like the currently used Obel lameness grading system does (TheHorse.com/31062).
“Only once we can recognize physiological and even emotional pain can we begin to treat it,” says Hector. “And once we begin to treat, can we do so better and sooner.”
1. Vivancos M, et al. Pharmacokinetics and bioequivalence of 2 meloxicam oral dosage formulations in healthy adult horses. Can Vet J. 2015 Jul; 56(7): 730-736.
2. Walliser U, et al. Evaluation of the efficacy of meloxicam for post-operative management of pain and inflammation in horses after orthopaedic surgery in a placebo controlled clinical field trial. BMC Vet Res. 2015; 11: 113.
3. Naylor RJ, et al. Comparison of flunixin meglumine and meloxicam for post operative management of horses with strangulating small intestinal lesions. Equine Vet J. 2014 Jul; 46(4):427-34.
4. Del Rio-Sancho S, et al. Topical delivery of diclofenac into and across equine skin from a novel liquid diclofenac epolamine formulation. J Vet Pharmacol Ther. 2016 Dec; 39(6):578-583.