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Omeprazole Use in Horses: New Lines of QueryBy Kentucky Equine Research Staff · September 14, 2016

Horses suffering from gastric ulcers benefit from the administration of omeprazole, a drug that decreases the production of stomach acid. Although omeprazole products labeled for equine use clearly indicate an appropriate dose, researchers* recently questioned those dosing guidelines, suggesting that diet and dose might not yet be optimized.

In their most recent study, Sykes and colleagues from the University of Queensland, Australia, and University of Liverpool, UK, wrote, “In humans, the effect of cumulative dosing, which results in an increased bioavailability over time, is well documented, yet conflicting evidence exists whether such an effect is present in the horse.”

Further, the impact of feeding and fasting on the availability of omeprazole (i.e., the amount of drug absorbed systemically that can ultimately exert an effect) remains unclear.

Researchers used six horses treated with either 1 mg/kg or 4 mg/kg of omeprazole while receiving either a high-grain/low-fiber diet or a diet comprised of free-choice hay. Not surprisingly, the “area under the curve,” or AUC, which is a measure of how much of the body is exposed to the drug after administration, was higher in horses treated with 4 mg/kg rather than 1 mg/kg of omeprazole. Although the AUC was higher in horses treated with omeprazole and fed a high-grain/low-fiber diet rather than hay, the difference between the two groups was not statistically significant. Further, there was a great deal of variability observed in the AUCs in the high-grain/low-fiber diet, suggesting that perhaps even though absorption of omeprazole in horses fed hay is lower than the high-grain/low-fiber diet, the absorption is more predictable and therefore desirable.

A cumulative effect of repeated omeprazole administration, such as increased bioavailability after several days of administration, did occur under certain conditions, but according to the researchers, data were variable and further investigation is needed.

“In addition to omeprazole, products such as RiteTrac, which contains both an antacid and a hindgut buffer to support gastrointestinal health, can help protect the sensitive lining of the equine stomach,” added Kathleen Crandell, Ph.D., an equine nutritionist with Kentucky Equine Research (KER). RiteTrac is available in the U.S. and other markets. Australian horse owners can try other research-proven products.

*Sykes, B.W., C. Underwood, R. Greer, et al. The effects of dose and diet on the pharmacodynamics of omeprazole in the horse. Journal of Veterinary Pharmacology and Therapeutics. In press.