Preliminary investigations into a novel, long-acting, injectable, intramuscular formulation of omeprazole in the horse

BackgroundPilot investigations have suggested that a novel, long-acting, injectable i.m. formulation of omeprazole (LA-OMEP) can induce acid suppression for up to 7 days following a single injection. ObjectivesTo investigate the pharmacodynamics and assess the clinical efficacy of the LA-OMEP formulation. Study designPart A comprised a pharmacodynamic study. Part B consisted of a pilot clinical trial. MethodsPart A enrolled six adult Thoroughbred horses with percutaneous gastrotomy tubes. Intragastric pH was measured for continuous 23-h periods (08.00-07.00 h) for eight consecutive days (days 0-7). A single 2.0-g dose of a 100 mg/mL LA-OMEP formulation was administered at 08.00 h on day 1. In Part B, 26 horses with squamous or glandular gastric disease were enrolled based on routine gastroscopic evaluation. Once enrolled, horses received 2.0 g of the 100 mg/mL LA-OMEP formulation by i.m. injection on days 0 and 7. Repeat gastroscopy was performed on days 14 (23 horses) or 16 (one horse). ResultsIn Part A, the percentage of time during which pH was above 4 exceeded 66% for days 1-4 in all horses and days 1-7 in four of the six horses studied. In Part B, healing was observed in all 22 (100%, 95% confidence interval [CI] 89-100%) horses with squamous disease and in nine of 12 (75%, 95% CI 47-92%) horses with glandular disease. Improvement, by at least one grade, was observed in all 22 (100%, 95% CI 89-100%) horses with squamous disease and in all 12 (100%, 95% CI 81-100%) horses with glandular disease. No worsening of lesions was observed. Lesion grade decreased over time in both the squamous (P<0.0001) and glandular (P = 0.0024) mucosa. Main limitationsSmall sample sizes. ConclusionsThe results of the present study compare favourably with previous reports on the pharmacodynamics of omeprazole and the clinical outcomes of trials reporting response to oral omeprazole therapy.