Abstract: Background – Gastric ulcers are common in horses. Long-acting injectable formulations of omeprazole might be more effective treatments than oral formulations. Hypothesis/Objectives - The objective was to evaluate the efficacy of long-acting injectable omeprazole on gastric ulcers induced by feed/fast/NSAID model. Animals – 12 clinically healthy, adult, university-owned Thoroughbred horses. Methods – A randomized, blinded, placebo-controlled clinical trial was performed. Horses were stall-confined for 30 days, intermittently fasted, and administered phenylbutazone from Days 0-7. On Days 0 and 7, gastroscopy was performed. Horses were allocated to treatment groups, injectable omeprazole (OMEIM) or saline control (CON). Treatments were administered on Days 7, 12, 17, and 22. Gastroscopy was repeated 5 days after each dose. Ulcers were scored by a masked investigator. Gastric pH was measured. Results – Ulcer scores were analyzed using the Friedman test with pairwise Dunn’s post-hoc comparisons within each treatment group. Non-glandular scores were significantly higher on Day 7 than Day 0. Groups were compared on each day using the Mann–Whitney test. Non-glandular scores were significantly lower in OMEIM than CON on days 22 and 27. Glandular scores were not significantly different between days or groups. Gastric pH was significantly higher in OMEIM than CON on Days 12, 17, 22, and 27. Horses maintained their body weight. Conclusions and Clinical Importance - Gastric pH was higher in OMEIM 5 days after starting treatment. OMEIM was efficacious against squamous ulcers induced by the model. Efficacy against glandular lesions could not be evaluated due to failure of the model to induce glandular lesions.
