It has been reported that more than 80% of highly trained horses will develop gastric ulcers. But only one anti-ulcer drug, GastroGard, has been found to significantly decrease the risk of developing moderate to severe gastric ulcers during training (see Research Reports, The Horse, August 2004, www.TheHorse.com/ViewArticle.aspx?id=2428). To compare the efficacy of less expensive pharmacy-compounded preparations of omeprazole and GastroGard, a group of scientists designed a study to compare the ability of GastroGard and three compounded preparations of omeprazole to maintain stomach pH at greater than 4.0 for a 24-hour period. The group was led by Alfred Merritt, DVM, MS, the Appleton Professor of Equine Studies and recently retired Director of the Island Whirl Equine Colic Research Laboratory at the University of Florida’s College of Veterinary Medicine.

A pH value of 4.0 was chosen based on research into human gastric esophageal reflux disease (GERD). “There is a large amount of evidence that gastric HCl (hydrochloric acid) is the primary ulcerogen (ulcer-causing substance) in horses, as in human GERD,” explains Merritt. Targeting human gastric pH at greater than 4.0 has found success in GERD patients, “so we aimed at keeping the pH greater than 4.0 for the better part of a day in our horses,” says Merritt.

Six horses with gastric cannulae (stomach tubes used to sample stomach contents) were given GastroGard or one of three compounded preparations of omeprazole in random order at 4 mg/kg body weight orally once daily for seven days. After a rest period of 14 days, another treatment was administered until all four treatments were applied to each horse. Gastric pH was continuously recorded via a probe inserted through the cannula during the day prior to treatment, and Days 2 and 7 after treatment.

The results indicated that only GastroGard and one compounded preparation (a suspension containing 50 mg omeprazole/mL) were capable of producing a significant change in the mean percentage of time that pH was greater than 4.0 during the 24 hours post-treatment, compared to baseline. Both GastroGard and the effective compounded version have high pH values (10.2 and 8.7, respectively) which might help explain these results. The acid-resistant coatings on GastroGard and the effective compounded version likely enhanced their bioavailability, as Merritt explains, allowing safe passage through the stomach and into the small intestine for absorption in their active forms