Impact of Dosage and Diet on Omeprazole Efficacy

Impact of Dosage and Diet on Omeprazole Efficacy

Sykes said the findings should not discount the importance of high-roughage diets for preventing squamous ulcers, but they do suggest that fasting overnight prior to drug administration could help maximize the chances of drug absorption.

Photo: The Horse Staff

When it comes to battling equine gastric ulcers, omeprazole is widely considered the go-to treatment. With this is mind, a team of researchers recently set out to examine diet and dosing’s impact on omeprazole’s efficacy in suppressing gastric acidity in horses in various scenarios:

  • With daily oral omeprazole doses of either 1 mg/kg or 4 mg/kg of body weight; and
  • In high-grain, low-fiber, or free-choice hay diets.

In this study, the team outfitted six healthy Thoroughbreds with percutaneous gastrostomy tubes (through the abdominal wall into the stomach) to measure gastric pH levels, first recording baseline levels on Day 0, then following up with measurements on Days 1-5 of omeprazole administration.

The research revealed two key findings, said lead researcher Ben Sykes, BSc, BVMS, MS, MBA, Dipl. ACVIM, ECEIM, PhD, of The University of Queensland in Australia.

“On one hand, when horses are consuming high-grain, low-fiber diets, and where they undergo a brief fast overnight, such as the typical racehorse diet, the 1 mg/kg dose was as effective as the higher dose in some horses,” he relayed. “This suggests that under such conditions, doses lower than the traditional treatment dose of 4 mg/kg may be equally effective in some horses.”

Sykes said this finding is consistent with a previous study he performed that suggested a dose of 1 mg/kg was as effective as 4 mg/kg in treating squamous ulcers under similar dietary conditions.

“The ability to use lower doses for therapeutic purposes, in some horses at least, may make treatment more affordable for many people, thus allowing the treatment of a greater number of horses,” he added.

The second key finding was that some horses’ response to omeprazole when consuming free-choice hay was much lower—sometimes even absent—even at the 4 mg/kg dose.

“In effect, some horses demonstrated minimal, if any, acid suppression despite five days of omeprazole at 4 mg/kg,” Sykes said. “This finding is somewhat against the current recommendations for the feeding of ad libitum hay.

"That is not to discount the importance of high-roughage/ad libitum hay diets in the prevention of squamous (ulcers), but what it does suggest, somewhat counterintuitively, is that during the treatment phase or where omeprazole is used prophylactically (as a preventive), it may be advantageous in some horses to enforce a brief period of fasting overnight prior to drug administration to maximize the chances of absorption. This would likely be especially true in horses that are not responding to conventional treatment and management regimens.”

As always, consult with your veterinarian to determine your horse’s best options. “The findings of this study suggest that the use of singular dosing regimens across all horse usage types may not be appropriate,” Sykes said. “Additionally, earlier work has highlighted that the individual responsiveness of different horses to omeprazole varies widely, a finding further supported by this study. I think that the best advice that I can give is to make sure to discuss your individual circumstances with your vet to ensure that you come up with a treatment plan that best suits your individual conditions and needs.”

He added that further research into preventing and treating gastric ulcers includes investigation into the use of alternative proton pump inhibitors (PPIs), such as esomeprazole, which is widely used in humans.

“We have conducted some work in this area focusing on different PPI formulations that would allow us to overcome the negative impact of feeding that we hope to publish soon,” Sykes said. “The ideal PPI would be highly effective regardless of the feeding state, allowing us to feed ad libitum hay and get good acid suppression at the same time, effectively giving us the best of both worlds.”

The study, “The effects of dose and diet on the pharmacodynamics of omeprazole in the horse,” was published in Equine Veterinary Journal

About the Author

Natalie DeFee Mendik, MA

Freelance journalist Natalie DeFee Mendik is a multiple American Horse Publications editorial and graphics awards winner specializing in equestrian media. She holds an MA in English from Colorado State University and an International Federation of Journalists' International press card, and is a member of the International Alliance of Equestrian Journalists. With over three decades of horse experience, Natalie’s main equine interests are dressage and vaulting. Having lived and ridden in England, Switzerland, and various parts of the United States, Natalie currently resides in Colorado with her husband and two girls.

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