Management of equine gastric ulcer syndrome (EGUS) is a hot topic, especially because EGUS is prevalent in a high proportion of horses across riding disciplines. As such, research is expanding on both squamous and glandular lesions. At the 2025 American Association of Equine Practitioners Convention in Denver, Colorado, Camilo Morales, DVM, MS, PhD, DACVIM, a current assistant professor at Auburn University, discussed a pilot study on vonoprazan, a new potential medication for treating EGUS. In humans, this drug is newly FDA-approved.
While omeprazole (OMP) is a proton pump inhibitor, vonoprazan is a potassium-competitive acid blocker that reduces gastric acid. It has a faster onset of action than OMP because it doesn’t require activation by acid. It is not affected by food or dependent on meal timing, and it provides a more consistent and longer acid suppression than OMP.
Pilot Study
In the initial pilot study, four horses received a single oral administration of either 0.5 mg/kg or 1 mg/kg oral vonoprazan under fed and fasted conditions to test for tolerance. The study progressed to phase two using six horses in a randomized four-way crossover design with a two-week washout between the various doses, medications, and placebo administration. All horses received all the tested treatments: Both doses of oral vonoprazan as well as 4 mg/kg oral OMP and a placebo to serve as controls. Researchers measured intragastric pH continuously for 24 hours. Horses had free-choice hay during the study.
Vonoprazan was well tolerated and well absorbed at both oral doses, and the initial study phase demonstrated short-term safety with good uptake. Phase two results demonstrated that 1 mg/kg achieves better results than 0.5 mg/kg. Treated horses had a consistently longer duration of gastric pH > 4 compared to pretreatment, which is the standard to determine ulcer healing. This study was conducted at the University of California, Davis.
Morales noted that a specific potassium-competitive acid blocker different than vonoprazan has been associated with liver disease in humans; more studies are needed for longer duration treatment in horses. Another noteworthy finding in humans is that vonoprazan might help manage glandular disease. In addition to not being FDA-approved, vonoprazan is currently cost-prohibitive, as one dose for a horse costs around $350.
Reference
Morales CJ, Sykes BW, McKemie DS, et al. Vonoprazan pharmacokinetics and effects on gastric pH following administration to fed and fasted horses. Equine Veterinary Journal Nov 2025; DOI: 10.1111/evj70128
In September 2026, Dr. Morales received the Peter Rossdale Equine Veterinary Journal (EVJ) Open Award for the referenced paper at BEVA Congress. The award and £1000 prize are given for the paper that best achieves EVJ’s mission to publish articles that influence and improve clinical practice and/or add significantly to the scientific knowledge that underpins and supports veterinary medicine in relation to the horse.
Related Reading
- Updates on Treatment of Equine Gastric Disease
- The Hindgut’s Role in Racehorse Health
- Cola Might Help Treat Gastric Impactions in Horses
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