You wake up a little stiff the morning after a hard ride. Thank goodness for ibuprofen--a couple of tablets and you're as good as new. But what about your horse? Is he stiff too? Perhaps a tablet or two of bute could help him just as much, but you're reluctant to take that step. Isn't bute a dangerous drug? Won't it cause your horse's stomach to rot and his kidneys to fail?
Wait just a minute. Although non-steroidal anti-inflammatory drugs (NSAIDs) do have their share of side effects, when used properly, they can help your horse just as much as that ibuprofen tablet helps you. And in many cases, they can help protect him against serious illness or injury.
In this article, I'm going to teach you the basics about NSAIDs. I'll tell you what they are, how they work and why they are such an important part of your horse's basic health care plan. I'll even outline potential toxicities and safe dosing protocols to ensure you use them safely. Once you understand the basics, I'll help you understand when and how to use NSAIDs with a set of common-sense scenarios.
What is Inflammation?
Inflammation is the response of living tissue to damage. For example, when blood rushes to the area, blood vessels become more permeable, and cells escape from the bloodstream into the surrounding tissues. Inflammation is characterized by redness, swelling, heat and pain.
- Redness: Inflamed tissue appears red because of the dilation of small blood vessels within the damaged area.
- Swelling: Edema resulting from accumulation of fluid in the inflamed tissues causes swelling.
- Heat: Temperature increases in damaged tissues because of increased blood flow to the area. In addition, chemicals released during inflammation can affect the body's temperature set point, resulting in an overall fever response.
- Pain: Pain occurs due to the stretching and distortion of inflamed tissues and to chemicals, such as prostaglandins, released during the inflammatory response.
Inflammation is often a major cause of discomfort when your horse is ill or injured. Prolonged inflammation can have long-term damaging effects.
NSAIDs include the drugs phenylbutazone (typically called "bute"), flunixin meglumine (brand name is Banamine®), ketoprofen (Ketofen®), meclofenamic acid (Arquel®) and acetylsalicylic acid (aspirin). As a group, these medications work by blocking enzymes in the body's pathway for inflammation. Specifically, NSAIDs inhibit the enzyme known as cyclooxygenase, which converts a substance called arachidonic acid into two other substances, prostaglandin and thromboxane. Prostaglandin and thromboxane mediate the body's inflammatory response.
When NSAIDs are administered, the effects of inflammation are controlled, and damage to the affected tissues is kept to a minimum. That means the redness, swelling, heat and pain in your horse's injured leg will be reduced. These drugs do this through a variety of mechanisms:
Relieving pain (analgesia): Prostaglandins produce pain by lowering the threshold of the C (nerve pain) fibers in your horse's body. By reducing prostaglandins, NSAIDs provide pain relief. It's interesting that these pain-relieving properties won't begin until the prostaglandins that formed before the drugs were given have dissipated--meaning there's a delay between treatment and effect.
Reducing fever (anti-pyretic): Prostaglandins produced during both infection and inflammation cause the temperature set point of the hypothalamus in your horse's brain to increase. By reducing prostaglandin production, NSAIDs help return the set point to normal, thus reducing fever. Your horse will benefit from the anti-pyretic effects of NSAIDs should he become ill with a virus or bacteria that causes his body temperature to rise. Reducing his fever makes him feel better and protects him from complications due to high body temperature.
Counteracting endotoxemia: Endotoxemia is a serious problem that occurs when your horse becomes ill and toxins are released into his bloodstream--often from the breakdown of normal bacteria that live within his body. These toxins result in elevations of blood lactate and plasma prostaglandins, and they can have life-threatening effects. Generally flunixin meglumine is the preferred NSAID for producing anti-endotoxic effects.
Reducing excessive blood clotting: Thromboxane helps with platelet aggregation (an anti-bleeding mechanism) and constriction of tiny blood vessels. By blocking thromboxane production, NSAIDs help maintain blood flow in situations where excessive blood clotting causes problems. For example, clots in blood vessels that supply your horse's gastrointestinal (GI) tract can lead to the death of portions of intestines due to lack of blood flow--a serious condition known as thromboembolic colic.
Although it's a weak anti-inflammatory medication in horses, aspirin has the most effective anti-platelet activity.
Although NSAIDs have many beneficial effects in conditions where inflammation leads to more serious problems, they do have their share of toxicities and risks. That's why it's so important that you learn to use them wisely.
First, some of the effects of inflammation are important protective mechanisms for your horse-most notably, pain. If in pain, he's not likely to use an injured limb. And if he's experiencing abdominal pain from colic, it's important that you monitor, not mask, that pain response in order to provide appropriate treatment. How can you minimize the risks of masking a more important underlying problem? Simple. Call your veterinarian before administering any NSAID. A thorough evaluation of your horse before you control signs of inflammation is critical to ensure you use them properly.
In addition to the risk of masking more serious problems with the use of these medications, be aware of the following potential toxicities.
Gastrointestinal tract: Prostaglandins protect your horse's GI tract by regulating blood flow and mucus secretion and by minimizing acids that affect the stomach lining. When NSAIDs block the damaging effects of prostaglandins, they also block these protective mechanisms, putting your horse at risk for developing ulcers throughout his GI tract. These GI risks occur whether you give NSAIDs by mouth or by injection. And although bute is thought to have the highest risk for causing ulcers, other NSAIDs can also cause these problems.
To avoid the risk of ulcers, be sure to maintain NSAID dosing within safe. In addition, take other steps to protect your horse against ulcer problems, such as feeding frequent meals and providing maximum pasture time.
Kidneys: Prostaglandins protect your horse's kidneys by regulating blood flow. This protection is especially important if your horse becomes dehydrated, because these prostaglandins ensure that adequate blood flow through the kidneys is maintained. If your horse is administered NSAIDs when he is dehydrated, this protection is lost and his kidneys can be damaged.
To avoid the risk of kidney damage, make sure your horse is well hydrated whenever he's administered an NSAID. For serious illnesses, your vet will generally avoid using these medications until your horse has been rehydrated with intravenous fluids.
Just Say "Yes"
Now that you know the basics about inflammation and the effects of non-steroidal anti-inflammatory medications, let's find out when and why NSAIDs are an important part of your horse's health care plan. The following scenarios will give you some practical examples of careful NSAID use.
Scenario No. 1: Your horse comes in from the pasture, and you notice that his right front leg is swollen and he's just a little bit off. He was fine this morning. You ice the leg and call your veterinarian.
The examination reveals that there are no abscesses within the foot that might be contributing to the swelling, no wounds that require further treatment and no signs of infection that might require antibiotics. An ultrasound examination shows that your horse has experienced a minor soft-tissue injury. Your veterinarian administers two grams of intravenous bute and leaves you with a prescription for this medication to use over the next few days. He recommends you continue icing, keep the leg bandaged and schedule a follow-up examination in two weeks to make sure the injury is healing.
NSAID benefits: The bute your veterinarian has administered and prescribed will immediately put a halt to the inflammatory response in your horse's leg. This means less swelling, less release of damaging enzymes to the area and perhaps a less serious injury as a result.
Scenario No. 2: Your 16-year-old Prix St. Georges horse is finally getting strong enough in the pirouette work that you think it's time to tackle Intermediaire I next year. It's true, he was diagnosed with arthritis in his hocks about five years ago, but along with careful training and conditioning, your vet has recommended a regular schedule of Adequan, Legend and a little bit of bute on hard training days.
NSAID benefits: The bute that you administer not only helps keep your horse comfortable and pain-free so he can continue work, but it also minimizes inflammation that could lead to additional problems. Because regular exercise is better for the horse with arthritis than a sedentary lifestyle, there's little concern about masking pain that could lead to more serious problems in the future. And, as long as you stay within safe dosing guidelines, take steps to minimize your horse's risk for gastric ulcers (such as maximizing pasture time) and maintain regular communication with your veterinarian, chances for toxicity or side effects are minimal.
Scenario No. 3: You toss your horse his morning hay, and notice that his eye is swollen twice its normal size. You flush it out with water and see that his eyeball looks gray. You call your vet immediately.
Your vet arrives on the scene and carefully examines your horse's eye. She stains the cornea (the clear outer layer) and determines that there's a scratch across the surface. She administers 500 milligrams of flunixin intravenously and prescribes regular doses of this medication to be given over the next few days. In addition, she leaves you with a number of different ointments that will help control pain and prevent infection of the damaged cornea.
NSAID benefits: The flunixin your veterinarian has used to treat your horse will reduce inflammation and help to minimize the accumulation of fluid within the cell layers that cause his cornea to appear gray. Some eye traumas can lead to an intense inflammatory response that can permanently damage the eye. The flunixin used in this situation helps reduce the chances of serious, long-term problems and provides much-needed pain relief.
Scenario No. 4: Your horse has been a little under the weather all day, and now he's refusing dinner. You noticed he was lying down a lot this afternoon--and he just started to paw and act uncomfortable. Uh oh! Colic strikes. You call your veterinarian. The vet examines your horse, including a full physical and rectal examination. He determines that your horse's colic is most likely the spasmodic type and suspects it will improve with medical treatment. He administers 300 milligrams of flunixin intravenously, which seems to control colic symptoms within about 15 minutes. He suggests you hold your horse off feed, monitor him carefully for signs of pain and keep in touch.
NSAID benefits: The flunixin your vet administered is a very potent pain reliever for colic symptoms and helps your horse feel better immediately. Notice that your vet has opted to administer a dose that's smaller than the maximum in order to minimize the chance that he'll mask painful symptoms should there be a more serious condition than the spasmodic colic he suspects. As an additional benefit, the flunixin's anti-endotoxic properties help protect your horse against this potentially life-threatening complication of a more serious colic event.
Barb Crabbe, DVM, is a graduate of the University of California at Davis. A lifelong horsewoman, she has earned her U.S. Dressage Federation (USDF) bronze medal. She is a USDF "L" graduate and has competed through Prix St. Georges. Based in Oregon City, Ore., she is in private practice at her Pacific Crest Sporthorses in Beavercreek.
For the complete feature story, see the May 2005 issue of Dressage Today magazine (subscribe now).