Pain Medications for Horses

Managing pain in horses is important for a lot of reasons: There are humane benefits in addition to medical ones, such as maintenance of weight, shorter hospital stays, and lower total patient bills. At the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla., Nora Matthews, DVM, Dipl. ACVA (anesthesiology specialist), professor of veterinary medicine at Texas A&M University, presented a review of pain medications commonly used to manage pain after operations and for chronic conditions.

"Early, aggressive treatment minimizes chronic pain, and early treatment requires less total drug," she noted.

Drugs are often combined in what's termed a balanced or multimodal approach in order to gain the benefits of multiple methods of action with lower doses and, ideally, fewer side effects. There are many ways to give pain medications to a horse, including the following:

  • Intravenously (IV);
  • Intramuscularly (IM);
  • Subcutaneously (SQ/SC);
  • Orally (PO);
  • Via epidural injection (into the spinal canal but outside the spinal cord);
  • Transdermally (through the skin); and
  • Through continuous rate infusion (CRI, which is an IV at a low, constant dose). Matthews described several drug classes and routes, individual drug options within those classes, and their benefits as follows.

Non-steroidal anti-inflammatory drugs (NSAIDs) These are effective for pain caused by inflammation and are often used in multimodal approaches. Common examples include phenylbutazone (Bute), flunixin meglumine (Banamine), meloxicam, carprofen, and the newer transdermally applied medication diclofenac (Surpass). Most can be used IV or PO, but they can have significant side effects, especially at high doses and when dehydration occurs. Transdermal NSAIDs carry a lower risk of side effects.

Opioids These medications act on the central nervous system to decrease pain perception and are often chosen for cases with severe pain. Common drugs include morphine, methadone, oxymorphone, butorphanol, fentanyl, and buprenorphine. Side effects can include gastrointestinal stasis (lack of motility) that can lead to impaction, bradycardia (slow heartbeat), hyperventilation, and excitation in nonpainful horses. Most are given IV, with some given SC, IM, or transdermally. Matthews noted that transdermals offer constant absorption of drugs over several hours, and noninvasive, targeted usage. However, their absorption depends on skin temperature, thickness, and hair coat.

Tramadol is a nonopiate drug that nevertheless works similarly to many opioids by stimulating the receptors for their compounds. It is available in generic form, but it is not yet approved for equine use. Matthews termed it "a promising drug."

Alpha-2 agonists These drugs have a short duration of analgesia and are primarily used for sedation by IV, IM, and PO routes, although epidural, CRI, and intra-articular methods have been used. Xylazine, detomidine, romifidine, and medetomidine are common choices.

Local anesthetics "We should never forget the locals," commented Matthews. "They can be used in a variety of ways." These medications are commonly used as nerve blocks for isolating pain in lameness cases as well as to desensitize areas for more invasive procedures. Lidocaine, mepivacaine, bupivacaine, and ropivacaine are common options.

Epidurals The epidural route is probably best known for its common usage to kill pain in women delivering babies. However, it's also used in horses for severe hind-end lameness. A catheter can be placed to allow intermittent dosing, or medication can be given one time. Morphine, ketamine, tramadol, xylazine, and detomidine can be used, but some loss of motor function might occur.

CRIs Several medications can be used via CRI; some are used to manage pain in cases such as burns and colics, while others can be used to manage pain and sedation for standing procedures. They often result in improvement of appetite and shorter hospital stays. Ketamine, butorphanol, detomidine, and medetomidine are common options.

Alternative therapies such as massage, acupuncture, or laser therapy might also help optimize pain control, she added.

"Combinations of different drugs seem to be most effective in providing pain relief while minimizing adverse side effects," she concluded. "Because each patient's pain is likely to be different, no one 'recipe' is appropriate for all patients; the veterinarian is encouraged to customize drugs based on the patient's response."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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