Phenylbutazone relieves inflammation and pain in horses. While effective, the therapy comes at a high price, as long-term phenylbutazone use can cause glandular gastric ulcers. To offset the risk of ulcers, veterinarians frequently recommend that phenylbutazone and omeprazole, a well-known acid suppressant, be given concurrently, though the safety and efficacy of this practice has not been documented.

To evaluate the effect of omeprazole on phenylbutazone-induced equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD), 22 horses with ulcers scores of 2 or less took part in a study at Louisiana State University.* In this study, an ulcer score of 0 indicated intact epithelium with no appearance of hyperkeratosis (squamous) or hyperemia (glandular); a score of 1 signified intact mucosa but areas of hyperkeratosis (squamous) or hyperemia (glandular); and a score of 2 denoted small single or multifocal superficial lesions.+

The horses were placed in one of three treatment groups for up to 14 days: phenylbutazone (4.4 mg/kg orally every 12 hours); phenylbutazone and omeprazole (4 mg/kg orally every 24 hours); or placebo. To track ulcers, gastroscopy was performed once a week. Complete blood counts and biochemistry were done before the study and at the end of the study.

The researchers found that omeprazole given concurrently with phenylbutazone protected horses from EGGD, likely due to an increase in gastric fluid pH, compared to phenylbutazone alone.

A complication of the coprescription of the two drugs arose, however. Increased incidence of intestinal problems occurred, specifically colic, impaction, diarrhea, and enterocolitis. Researchers theorized complications may have been due to microbiome disturbance, changes in intestinal motility, and intestinal inflammation.

The researchers pointed out that while the dose of phenylbutazone used in the study would be considered high, it is not outside the realm of clinical practice.

Caution should be exercised when coprescribing nonsteroidal anti-inflammatory drugs (NSAIDs), like phenylbutazone, and omeprazole in horses, particularly in association with changes in management, summarized the researchers.

“Phenylbutazone, or bute, and other NSAIDs are here to stay for the foreseeable future, as they are well-established medications for certain ails,” said Catherine Whitehouse, M.S., a nutrition advisor at Kentucky Equine Research. “A study in 2019, for example, found that bute was the NSAID most often prescribed for orthopedic pain. With this in mind, the question then becomes how best to protect the gastrointestinal tract when bute must be used.”

Veterinarians reach for omeprazole to heal ulcers, but there are other ways to help protect the stomach, not just in times of high susceptibility but every day. “Choosing a high-quality digestive supplement can help both the gastric and hindgut environments remain healthy when NSAIDs must be used,” Whitehouse said.

*Ricord, M., F.M. Andrews, F.J. Yñiguez, M. Keowen, F. Garza, Jr., L. Paul, A. Chapman, and H.E. Banse. 2021. Impact of concurrent treatment with omeprazole on phenylbutazone-induced equine gastric ulcer syndrome (EGUS). Equine Veterinary Journal 53:356-363.

+Sykes. B.W., and J.M. Jokisalo. 2014. Rethinking equine gastric ulcer syndrome: Part 1 – Terminology, clinical signs and diagnosis. Equine Veterinary Education 26(10)543-547.

°Duz, M., J.F. Marshall, and T.D. Parkin. 2019. Proportion of nonsteroidal anti-inflammatory drug prescription in equine practice. Equine Veterinary Journal 51:147-153.