Gastric ulcers in horses are caused by prolonged exposure of the gastric mucosa to gastric acids. This syndrome, also called Equine Gastric Ulcer Syndrome or EGUS, results in ulceration and bleeding in some instances. A horse’s stomach essentially has two sections: an upper non-glandular region where food enters the stomach, and a lower glandular region where hydrochloric acid (HCl) is produced.¹ While the lower region is constantly exposed to gastric acids, it generally has adequate protection from these acids; thus, lesions are most commonly found in the upper region. 

EGUS is most closely associated with performance horses, horses that have been stressed over a protracted period of time, and horses that were sick to start with. Its prevalence in unmedicated racehorses in active training is at least 90%, whereas in non-racing performance disciplines, its prevalence is over 60%.¹ Foals are known to be at high risk for development of perforating peptic ulcers until they are several weeks old due to the undeveloped state of their gastric mucosa. While spontaneous remissions of these lesions have been described in the literature, horses that remain in situations tending to give rise to this malady are likely to remain ill without medical intervention.

Stress is also believed to be a major contributor to EGUS. Transportation, stall confinement and the rigors of performance (where performance horses are involved) are all additional risk factors for EGUS. Finally, the repeated administration of nonsteroidal anti-inflammatory drugs (NSAIDs) can impede the production of mucus in the stomach, making the horse far more susceptible to ulcers.²

Gastric Ulcers in Horses: Clinical Signs 

Most horses suffering from gastric ulcers do not exhibit overt clinical signs; often, these horses appear completely healthy. Some of the more subtle signs of EGUS can include:

• Poor appetite
• Weight loss
• Dullness
• Changes in mood and/or behavior
• Decreased performance
• Reluctance to train
• Poor body condition
• Dull coat
• Colic

In foals, the clinical signs of ulcerative disease include intermittent colic, frequent recumbency, reduced nursing, diarrhea, poor appetite, a pot-bellied appearance, grinding of teeth, and excess salivation.³ If a foal exhibits clinical signs, the ulcers are likely to be severe and should be diagnosed and treated immediately.

Gastric ulcers can only be diagnosed definitively through endoscopy. This involves inserting the endoscope into the stomach and performing a visual examination of the stomach mucosa. The procedure is minimally invasive, produces minimal stress in the horse and allows for examination of the esophagus, stomach, and small intestine.²

Treatment of EGUS in Horses

Omeprazole is useful in the treatment of both gastroduodenal ulcer disease and prevention or treatment of gastric erosions caused by ulcerogenic drugs (eg, aspirin, NSAIDs).

Omeprazole is usually sold as a paste or powder formulation and has been very effective in preventing and treating gastric ulceration in all types of horses. Since the commercial paste is on the expensive side, some compounding pharmacies prepare and sell paste or liquid omeprazole at lower prices.³ Preventative doses of omeprazole are commercially available for use in transportation or stressful events. It is believed that horses with a history of gastric ulceration can benefit from proactive treatment to decrease the chances of ulcer formation or recurrence.

Cimetidine for the Treatment of Equine Gastric Ulcers

Cimetidine is a prototype histamine₂-blocker primarily used to reduce GI acid production. In veterinary medicine, cimetidine has been used in the treatment and/or prophylaxis of gastric, abomasal, and duodenal ulcers, uremic gastritis, stress-related or drug-induced erosive gastritis, esophagitis, duodenal gastric reflux, and esophageal reflux. It has also been employed to treat hypersecretory conditions associated with gastrinomas and systemic mastocytosis,⁵ and as an adjunctive treatment for melanomas in horses.

Cimetidine competitively inhibits histamine at the H₂ receptors of the parietal cells, thereby reducing gastric acid output both during basal conditions and when stimulated by food, pentagastrin, histamine, or insulin.³ Gastric emptying time, pancreatic or biliary secretion, and lower esophageal pressures are not altered by cimetidine. By decreasing the amount of gastric acid secretions, cimetidine also decreases pepsin secretion. Cimetidine has an apparent immunomodulating effect, as it has been demonstrated to reverse suppressor T-cell-mediated immune suppression. It also possesses weak anti-androgenic activity.⁵

Cimetidine is a CLASS 5 DRUG under the Association of Racing Commissioners International (ARCI) Uniform Classification Guidelines for Foreign Substances (UCGFS).

Where to buy Omeprazole + Cimetidine

Omeprazole + Cimetidine is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. 

This product carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Young, A. Equine Gastric Ulcer Syndrome. In: Journal UC Davis School of Veterinary Medicine, July 29, 2019. 

²Andrews, F. Gastric Ulcers in Horses. In: Merck Veterinary Manual, Jan. 2014.

³Loving, N. Research on Treatment of Equine Gastric Ulcer Syndrome. In: EquiManagement.com, Jan 13, 2019.