Effects of Common Horse Show Medications (Phenylbutazone, Dexamethasone, and Esomeprazole) on Gastric pH and Ulcer Development Under Show-Like Conditions

Introduction: Performance horses are at high risk for equine gastric ulcer syndrome (EGUS). The use of common horse show medications (phenylbutazone and dexamethasone) may exacerbate EGUS development. Esomeprazole is effective in horses, can treat ulcers more effectively than omeprazole in people, and has intravenous (IV) and oral formulations.

Materials and Methods: Over two phases, six adult horses received phenylbutazone (bute; 2 g SID) administered on days 1 and 2, bute and dexamethasone (dex; 10 mg SID) administered on days 3 and 4, and bute, dex and esomeprazole (IV or oral, randomized crossover design; 0.5 mg/kg) administered days 5 and 6. Gastric juice pH was measured daily, on day 7, and 1 hour after each new drug was introduced. Squamous and glandular ulcers were scored every other day (days: 1–7). Data was analysed using mixed model analysis for repeated measures, with significance at p ≤ 0.05.

Results: Squamous ulcer scores increased from day 1 (2.00 ± 0.63) to days 5 (2.67 ± 0.52) and 7 (3.33 ± 0.82; p ≤ 0.04) and from days 3 (2.5 ± 0.55) and 5 (2.67 ± 0.52) to day 7 (3.33 ± 0.82; p ≤ 0.04). Glandular ulcer scores increased from day 1 (0.33 ± 0.52) to day 7 (1.50 ± 1.22; p = 0.04). Esomeprazole increased pH 1 hour after its administration (p = 0.009). When separated by treatment, pH increased in horses receiving IV (p ≤ 0.04), but not oral, esomeprazole. However, there were no differences between IV and oral treatments in pH and ulcer scores.

Discussion/Conclusion: Ulcer scores increased significantly with the administration of bute and bute/dex. Esomeprazole was effective at increasing gastric pH but did not prevent an increase in EGUS.

Acknowledgment

Funding was provided through the Center of Excellence Summer Veterinary Scholars Research Program. The authors would like to thank Layla Gray, Dr. Xan Carlson, Sarah Desai, Ellie Lewis, Chessa Brown, and Amanda Womble for assistance with data collection.

 

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Publication History

Article published online:
15 July 2025