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If you’ve ever had to deal with equine gastric ulcers, you—and your wallet—will likely be happy that researchers have learned that a much lower dose of one omeprazole formulation could be just as effective in treating the condition as the standard dose.

“Our study showed that lower doses are equally effective for the formulation used and under the conditions studied, even when used at 1 mg/kg,” said Ben Sykes, BSc, BVMS, MS, Dipl. ACVIM, ECEIM, MBA, of BW Sykes Consultancy in New South Wales, Australia. Sykes collaborated with Gayle Hallowell, MA, VetMB, PhD, CertVA, Dipl. ACVIM-LAIM, ACVECC, FHEA, MRCVS, associate professor at the School of Veterinary Medicine and Science at the University of Nottingham in Sutton Bonington, U.K.

That low dose—1 mg/kg—is one quarter the standard dose of omeprazole for treating gastric ulcers, Sykes said. “There is unquestionably a financial benefit if lower doses can be used,” he said, “as this would increase the number of owners that can afford treatment and, thus, the number of horses that can be treated.”

In their study, Sykes and his fellow researchers monitored 60 Thoroughbred racehorses confirmed by gastroscopy to have gastric ulcers. The horses were randomized into three treatment groups: 1 mg/kg, 2 mg/kg, or 4 mg/kg (the standard dose) of a commercially available, enteric-coated omeprazole paste (Gastrozol, manufactured in Australia by Axon Animal Health). Treatments were given before meals and exercise. After 28 days, horses received a follow-up gastroscopy to see if treatment was effective.

They found that all three treatment groups were equally effective in reducing ulcer scores and leading to healing, he said.

However, regardless of the dose, ulcers in the glandular region of the stomach did not respond as well as ulcers in the squamous section, he added. The equine stomach is composed of two sections of stomach wall: the acid-producing glandular region, and the smooth squamous region that has a lining similar to the esophagus. While traditionally veterinarians believed most ulcers occurred in the squamous region, it is becoming increasingly apparent that ulcers can affect the glandular region as well.

“The healing response of glandular ulceration was vastly inferior to that of squamous ulceration,” Sykes said.

In fact, as many as 36% of the glandular ulcers actually worsened over the 28 days of their study, without any association to the dose level. “This is very frustrating for veterinarians and owners alike. It has certainly reinforced the need for us to be specifically discussing whether we are treating/talking about squamous or glandular disease rather than relying solely on the over-reaching term equine gastric ulcer syndrome to describe both conditions.”

The lower doses' efficacy against squamous ulcers might have had something to do with the treatment's timing, Sykes said. The team administered omeprazole to the study horses on an empty stomach, which might have helped the absorption. Researchers took advantage of a short fasting period between feedings, he said. But he would not recommend purposefully fasting a horse with ulcers, because hay acts as a buffer in the stomach to prevent damage from acids. This is especially important once treatment has ended, he added.

Lower-dose efficacy might also be due to the study treatment preparation, Sykes said. All treatments, regardless of dose, consisted of enteric-coated omeprazole granules in paste. The water-soluble coating (like a capsule) is designed to protect the omeprazole from acidity in the stomach and delay its release. This presentation differs slightly from that of the commercially available, U.S. FDA-approved omeprazole formulations, which are suspended in a buffer as protection instead, he said.

“Manufacturers of enteric coated formulations claim higher bioavailability” which might explain the efficacy of lower doses, he said although an initial study of bioavailability showed only a “modest” improvement of 25%.

Even so, there’s a limit to how low the dose can go, Sykes said. In further research he found that very low doses result in lower success rates. “What we need to do now is further investigate where that threshold between the lowest effective dose and good efficacy is found,” he said.

The study, "A comparison of three doses of omeprazole in the treatment of equine gastric ulcer syndrome: A blinded, randomised, dose-response clinical trial," will appear in an upcoming issue of the Equine Veterinary Journal.