Phenylbutazone (“bute”) is an anti-inflammatory drug — a non-steroidal anti-inflammatory similar to aspirin, Advil, Motrin, Banamine, etc. Bute has been used for decades in horses to relieve pain, particularly in musculoskeletal injuries, navicular syndrome, arthritis, and so on. Melinda Freckleton, DVM (Haymarket, Virginia) says this is a drug that’s used frequently and is a comparatively safe and effective way to reduce pain and inflammation.
Veterinarians prescribe it for a wide number of problems, but horse owners should be aware of possible side effects, just like when using pain relievers in humans. “Even though most humans can tolerate a little aspirin or ibuprofin once in awhile, there are a few individuals who cannot use these. The same is true with horses and bute. There are also some risks when using these drugs inappropriately — such as at too high a dose or for too long a duration,” she says.
“This is why there are specific dosing recommendations. Horse owners need to realize that even though the drug is helpful, giving more than the recommended dose won’t give more benefit. Several studies have shown that there are diminishing returns when increasing the dosage. On a practical basis, one gram will give a certain amount of pain relief, and 3 grams will not give you more,” explains Freckleton.
Giving an increased dose will, however, result in more side effects (and may be dangerous to the horse). Horse owners should try to administer the lowest dose that gives benefit to the horse. Giving more may cause more adverse reactions. These side effects include gastric ulcers, kidney dysfunction, and occasionally right dorsal colitis.
Gastric ulcers are the most common risk. “There are certain horses that probably won’t get gastric ulcers no matter what we do to them (similar to certain humans who can tolerate continual use of aspirin with no problems). But often the horses receiving the most bute, the most frequently, have other risks at the same time (such as stress, pain) that also make them more prone to ulcers. A drug like bute is a risk factor for gastric ulcers, but so is any kind of physiologic stress. This could include the condition you are treating, or even being confined in a stall. Often whatever painful condition you are treating requires you to confine the horse or change its routine and restrict its activity,” she says.
Thus the risks are often multiplied. “Horses at risk for gastric ulcers should probably receive a different drug, or we might in addition to the bute give a gastric protective product, such as omeprazole (Gastrogard or Ulcergard) or ranitidine (a generic ulcer treatment),” says Freckleton.