A study published in the November Journal of the American Veterinary Medical Association really drives home the risk of damage to the colon from phenylbutazone use.
Twelve healthy adult horses were given the upper normal dose of phenylbutazone (about 4 grams/day for most horses) for 21 days. Two of the horses developed colitis, and all of them had evidence of subclinical colitis with ”leakage” of blood protein/albumin into the colon, a drop in neutrophil counts, and increased arterial blood flow to the colon. The drug also influenced fermentation of fiber in the colon, with a drop in the volatile fatty acid acetate, a by-product of fermentation that is an important energy source for horses.
Phenylbutazone is an effective and inexpensive anti-inflammatory drug in horses but, as with any drug, it comes with a benefit versus risk profile. It is meant to be used only for short term, days not weeks or months. In addition to negative effects on the stomach and colon, phenylbutazone is well documented to interfere with soft tissue and bone healing.
In the normal course of recovery from a traumatic or surgical injury, the acute inflammatory response, and therefore the worst of the pain, should be gone in 3 to 5 days. If it’s not, veterinary reevaluation to find out why is indicated. You can also decrease the need for pain medications by using ice or cold water and alternative topical anti-inflammatories like Sore No-More liniment (see page 3 for article on liniments).