Pain Management Options for Horses

Methods of managing pain in horses range from non-steroidal anti-inflammatory drug use and opioids to α-2 agonists and ketamine, among others. Over the years, experience and research have helped veterinarians determine which of the numerous analgesics (painkillers) are most effective. During a presentation at the 2011 Western Veterinary Conference, held Feb. 20-24 in Las Vegas, Nev., Khursheed Mama, DVM, Dipl. ACVA, a professor of veterinary anesthesiology at Colorado State University, discussed the different analgesic (pain management) options available and how effective they generally are for treating horses' pain.


"Non-steroidal anti-inflammatory drugs (NSAIDs) have been the mainstay of equine analgesia for many years," Mama said, noting that phenylbutazone (Bute) and flunixin meglumine (Banamine) are the two most commonly used drugs in this category. Veterinarians employ these successfully to treat a variety of ailments in horses, including gastrointestinal, musculoskeletal, and ocular (eye) pain. Practitioners use other NSAIDs (e.g., ketoprofen and carprofen) on a less common basis to treat similar disorders.

She added that recent research showed that a topical NSAID (1% diclofenac sodium, Surpass) was effective in treating localized pain and inflammation with limited to no side effects. Mama noted one study in which up to 74% of horses tested showed an improvement in mobility and a reduction in lameness and pain when treated with this drug. She added, however, that the study's control group (which received a placebo ointment) also demonstrated a 40% improvement.

Mama explained that while NSAIDs are lumped into one category, it's important to remember that each drug has its own chemical composition and level at which it causes toxicity. Toxicity generally results from overdosing the horse with medication, she said, and most episodes affect the gastrointestinal tract, kidneys, or liver.

"Neonatal patients appear to be more susceptible to these undesirable effects," she added.


Mama moved on to another class of medications: "While there is reason to believe opioid drugs should have analgesic actions in the horse, reports regarding their efficacy are mixed," Mama said.

Veterinarians frequently use opioids such as morphine or butorphanol with sedatives or tranquilizers when performing procedures in standing horses. These combinations are thought to be especially useful when working around the hind legs as they seem to minimize the likelihood of the horse kicking, Mama added. However, their efficacy as analgesic medications is mixed, she noted.

Some studies suggest that pain relief is afforded by these drugs for short periods of time or when given by infusion. However, some of the side effects of opioid drugs in horses--such as gastrointestinal stasis (lack of motility), and arousal (hypersensitivity to surroundings)--might preclude veterinarians from using opioid drugs.

Mama noted that opioids appear to be more effective when administered epidurally than when given systemically. While morphine is most commonly used via this route, Mama explained, hydromorphone noted to begin working in 20 minutes when administered epidurally. Meperidine similarly is reported to work within 12 minutes following epidural administration. She added that opioids have been documented to be effective for pain relief when given as intra-articular injections to humans and other domestic animals, and she believes there might be a similar effect in horses.

α-2 Agonists

"α-2 agonists are perhaps the most effective systemically used analgesics in the horse, as evidenced by both laboratory studies and clinical use," Mama said, although she added that they typically are not the first choice for analgesics as they can produce side effects including ataxia (incoordination), drowsiness, hyperglycemia (an elevated level of blood glucose), and gastrointestinal stasis, among others.

Veterinarians typically use α-2 agonists to sedate horses for standing procedures and also before putting horses under general anesthesia. Mama added that α-2 agonists are commonly used to sedate (and thus control the pain) of horses that present with clinical signs of colic.

She discussed a relatively new α-2 agonist gel formulation of detomidine introduced to the market for sedation. She said the oral gel seemed to provide adequate sedation for nonpainful procedures beginning an average of 36 minutes after administration, with sedation lasting for about two hours. She added that further evaluation is needed to determine the effect of the oral gel for analgesia or as a sedative for "painful procedures such as suturing a laceration or tooth extraction."


Next, Mama explained how veterinarians have considered ketamine as an equine pain management option. Some researchers have suggested that ketamine prevents the upregulation (an increase in a cellular response to a molecular stimulus due to increase in the number of receptors on the cell surface) of neuronal pathways involved in further sensitizing the horse to painful stimuli (simply put, it prevents an increase in pain within the horse's body).

"While (ketamine's) efficacy for this purpose has not been assessed in horses, evidence from people (human patients) and more recently dogs suggests that very low doses may not only prevent 'wind up' (sensitization) but also provide relief in patients with chronic pain syndromes where other drugs are not effective," Mama said.

Other Analgesic Drugs

Mama briefly discussed the use of local anesthetics, gabapentin, and tramadol.

Practitioners use local anesthetics (such as lidocaine and carbocaine) regularly for regional anesthesia in horses. Mama noted that the use of intravenously injected lidocaine has also been used to provide pain relief and has been shown to reduce the dose of sevoflurane (an inhaled anesthetic) in horses. However, she added that how and why this works is still unclear.

Gabapentin, though not currently widely used in horses, is being used in humans and small animals to treat neuropathic pain (caused by damage to the peripheral nerves, or the spinal cord). Gabapentin is absorbed following oral administration to horses. Mama explained that one case report indicated that gabapentin yielded "marked improvement" in treating neuropathic pain in a pregnant mare following colic surgery.

Finally, Mama said that tramadol (which is related to codeine) is thought to have weak opioid properties. She explained that the only form of the drug available in the United States is the oral form, and studies on whether this form is effectively absorbed in the horse have yielded conflicting results. A number of side effects have been noted after intravenous tramadol administration, including collapse, trembling, sweating, and excitement. She suggested that further research is needed to determine if this drug will have a place in equine medicine.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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