Effect of GastroGard and three compounded oral omeprazole preparations on 24 h intragastric pH in gastrically cannulated mature horses.
Authors: Merritt A M, Sanchez L C, Burrow J A, Church M, Ludzia S
Journal: Equine veterinary journal
Summary
# Editorial Summary: Omeprazole Efficacy in Horses Equine gastric ulcer syndrome (EGUS) affecting the squamous mucosa remains a significant concern in intensively trained horses, yet therapeutic options have received limited rigorous evaluation beyond the branded formulation GastroGard. Merritt and colleagues conducted a controlled trial using six gastrically cannulated horses to directly compare intragastric pH suppression across GastroGard and three pharmacy-compounded omeprazole preparations, each administered at 4 mg/kg once daily in a randomised crossover design with continuous 24-hour pH monitoring on days 2 and 7 of treatment. Only GastroGard and one compounded preparation significantly elevated mean intragastric pH above 4.0 for at least 12–14 hours post-administration on both measurement days; critically, both effective products had vehicle pH exceeding 8.0, whilst the two ineffective compounds had vehicle pH below 6.0, suggesting formulation composition—rather than omeprazole dose alone—directly influences clinical efficacy. These findings indicate that not all generic omeprazole compoundings will reliably prevent squamous ulceration, and practitioners selecting off-label preparations should specifically verify vehicle pH and request in-vitro or clinical efficacy data. For athletic horses, administering an effective omeprazole preparation 4–8 hours before training may optimise acid suppression during the high-risk training window, though formulation quality remains the critical determinant of therapeutic success.
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Practical Takeaways
- •Not all generic omeprazole preparations are equally effective—GastroGard and specifically formulated high-pH compounded versions work best; verify your compounded omeprazole has vehicle pH >8.0
- •For horses in intensive training, administer omeprazole 4-8 hours before training sessions rather than at arbitrary times to optimize gastric acid suppression during work
- •A single daily dose of 4 mg/kg omeprazole provides adequate gastric protection for at least 12 hours, making once-daily dosing practical for field management
Key Findings
- •GastroGard and one compounded omeprazole preparation maintained intragastric pH >4.0 for at least 12-14 hours post-administration on Days 2 and 7, while two other compounded preparations were ineffective
- •Vehicle pH >8.0 was associated with effective omeprazole preparations, while vehicle pH <6.0 was associated with ineffective preparations
- •Omeprazole at 4 mg/kg once daily can effectively maintain anti-ulcerogenic intragastric pH levels in mature horses for at least 12 hours post-administration
- •Optimal dosing timing for athletic horses should be 4-8 hours prior to training sessions to suppress gastric squamous ulceration