A long-acting, injectable form of omeprazole may be available for horses soon, according to an Australian researcher who recently completed an efficacy study of the drug.
First developed as a human medicine, omeprazole is used to treat and prevent gastric ulcers in horses. The medication is currently available only in an oral paste formulation that must be administered daily. The new omeprazole formulation is injected intramuscularly every seven days. In addition to less frequent administration, the injectable form of the drug offers other benefits, says Ben Sykes, BVMS, PhD, of the University of Queensland.
“The use of an intramuscular formulation bypasses the problems observed in some horses with very low absorption of omeprazole, especially in horses consuming free-choice hay diets---this would be a key advantage,” says Sykes (see “Effects of Diet on Ulcer Treatment Studied,” Medical Front, EQUUS 472). “But we also saw higher healing rates in a shorter period of time than previously reported with the oral formulations.”
The study was conducted in two phases. For the first half, Sykes and fellow researchers monitored the stomach pH levels of six racing Thoroughbreds for seven days after an omeprazole injection. On the pH scale, a score of 7 is considered neutral, and the lower the score the more acidic a substance.
The data showed that during the first four days after omeprazole injection all of the horses had a gastric pH of ≥4 at least 66 percent of the time, and four of the six exceeded that level for seven days. That 66 percent threshold is considered a significant indicator of gastric healing in people with gastric reflux, explains Sykes, adding that previous research showed that, on average, horses had a gastric pH of ≥4 for as little as 30 to 40 percent of the time by the fifth day after administration of oral omeprazole.
For the second half of the study, 26 Thoroughbreds with confirmed gastric ulcers were given two omeprazole injections, one week apart. Each horse’s ulcers were viewed using a gastroscope and scored before treatment began and again at the end of the two-week study period. Improvement, by at least one grade, was seen in every horse during that period.
In fact, the ulcers were completely healed in all of the horses who had squamous lesions (found in the top portion of the stomach) and in 9 of 12 horses with glandular lesions (found at the bottom portion). By comparison, healing rates among horses given only oral omeprazole range from approximately 25 percent for glandular lesions and 70 to 85 percent for squamous lesions, after 28 to 35 days of daily treatment.
“The results of this study are particularly promising as, to date, the reported response rates for equine glandular gastric disease (EGGD) have been frustratingly poor,” says Sykes. “The idea of being able to reliably induce acid suppression, regardless of diet, and to potentially treat horses more effectively and in a shorter time is very exciting.” He adds that “the formulation is currently in the process of commercialization and it is anticipated that it will be available in several key markets mid- to late 2017.”
Reference: “Preliminary investigations into a novel, long-acting, injectable, intra-muscular formulation of omeprazole in the horse,” Equine Veterinary Journal, April 2017
This article first appeared in the July 2017 issue of EQUUS (Volume #378)