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Vet Talk

Use of NSAIDs in Horses is Tricky
August 6, 2012 (published)

The following scene unfolded in our office on an almost weekly basis:

Client – Hi, I need to get some Bute for my horse.

Office Manager – Ok, what’s your name and your horse’s name?

Client answers. Office manager pecks frantically at keyboard.

Office Manager – I’m not seeing this horse under your name. Is there another file he might be in? Which doctor saw him last, and what were they prescribing the Bute for?

Client – Oh, he hasn’t been to the vet in years. I just give him a couple Bute tablets now and again and he does just fine. But I finished off the bottle I got from old doc down the road, and since he’s closed now, I need to get some more from you guys.

Office Manager – I’m sorry, but we can’t give you any Bute without a prescription from one of our doctors. I can set up an appointment for an exam if you’d like.

Client – What do I need an exam for? He’s fine so long as he gets his Bute. But I ran out a couple days ago and he’s getting pretty stoved up now.

Office manager refrains from beating her forehead bloody against the keyboard.

Bute, or phenylbutazone, is arguably the most common drug in the equine veterinarian’s arsenal. Half-used tubes of Bute are more common in barns than mice. Widely used for decades, primarily to treat musculoskeletal pain, phenylbutazone is a reliable analgesic (painkiller) and anti-inflammatory in horses. It is so familiar to horse owners that many have trouble wrapping their neurons around the fact that this medication is not available over the counter.

Phenylbutazone is classified as a non-steroidal anti-inflammatory drug (NSAID). While a number of human NSAIDs (ibuprofen, naproxen, etc) are available as over-the-counter drugs, this is not the case in veterinary medicine. Despite being widely used for decades, the most common equine NSAIDs – phenylbutazone, flunixin meglumine (Banamine), firocoxib (Equioxx), and diclofenac (Surpass) – are available by veterinary prescription only

Why? For the good of the veterinarian’s bank account? Nah. Realistically, if we were just after your money, why wouldn’t we sell you any drug on demand without risking turning you away by saying no? How often does Wal-Mart say, “No, sorry, you can’t buy that from us?”

I say this on behalf of office managers, technicians, receptionists, and beleaguered equine veterinarians everywhere: These rules are in place for the benefit of your horse.

NSAIDs are tricky things. These medications are great at doing their job of interrupting the inflammatory cascade. When an animal experiences an inflammatory event – usually associated with trauma or infection – a series of chemicals called inflammatory mediators are released in response to each other. Think of the inciting event (infection, trauma, etc.) as a poking finger and the inflammatory cascade as a row of dominos. NSAIDs step in front of the domino called COX, stopping it from continuing the cascade. Now here’s the catch: That domino cascade isn’t one long line. It divides into two pathways at COX. COX-1 and COX-2 (not to be confused with Dr. Seuss’s Thing One and Thing Two) each promote the release of chemicals called prostaglandins. Certain prostaglandins such as prostaglandin F2–alpha produce the sensations of pain and inflammation that we - and our horses - find undesirable. However, certain “good” prostaglandins promote blood flow to, and are protective of, organs such as the kidney and the lining of the stomach and intestines.

COX-1 pushes down the domino row leading to the “good” prostaglandins, while COX-2 activates the “bad” prostaglandins. Most NSAIDs that are commonly used in horses block both COX-1 and COX-2.

You still awake? We’re getting to the punch line. 

Most of the adverse side-effects associated with NSAIDs result from inhibiting COX-1 enzymes. Even though we’re trying to block COX-2, NSAIDs such as Bute and Banamine stand in the way of both COX-1 and 2. So, yes, we block the pain and inflammation with these drugs, but we also potentially impact blood supply to vital organs.

Like snowflakes, horses are individuals. Horses don’t read package inserts and they don’t care which statistical category they fall under. This individual variation makes predicting which animals could have an adverse reaction to a drug tricky – a lot tricky. 

Does this mean you should never give your horse any medication, but should instead chant Hannibal ante portus while circling your horse backwards three times under a full moon and in a sage bush? No. (I like the image, though. Do that again, would you?)

It does mean that use of NSAIDs should be handled carefully: with proper supervision, accurate, evidence-based dosing - not “Well, I’ll give him a handful now because he looks sad” - and with a good understanding of the horse’s physiologic condition. In other words, NSAIDs should be given on the recommendation of a veterinarian with current and accurate knowledge of the individual horse and of the specific condition being treated. 

Circumstances can also alter how the body processes medication. Conditions such as dehydration can drastically increase the risk of an adverse reaction to NSAIDs. If your horse is not eating or drinking, or has a lapse in access to water while taking an NSAID, you need to contact your vet. Similarly, if your horse begins to show signs of diarrhea, colic, or loss of appetite while on one of these medications, let your vet know.

Remember, only YOU can prevent forest fires. Oh, wrong public service announcement, sorry.

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