Clinical efficacy, safety and pharmacokinetics of a novel long‐acting intramuscular omeprazole in performance horses with gastric ulcers

Abstract

SummaryOral omeprazole is used in the management of equine gastric ulcer syndrome (EGUS). However, its use may have limitations with regard to individual variation in absorption and the impact of dietary management on bioavailability. The objective of this study was to determine whether a novel compounded long‐acting injectable omeprazole (LAO‐USA) formulation would provide consistent serum omeprazole concentrations and to determine whether it was clinically safe and efficacious in the reduction of EGUS. Twenty‐three horses with EGUS described as having evidence of equine squamous gastric disease (ESGD) and/or equine glandular gastric disease (EGGD) received a 5 mg/kg bwt intramuscular injection of LAO‐USA once every 7 days for four doses. Gastroscopy was performed prior to the study and at Days 14 and 28. Pharmacokinetic analysis was performed to determine omeprazole concentrations over 7 days. Safety was measured by monitoring injection site reactions daily and bloodwork screening prior to and following the study. Of the horses with ESGD, 78% had improvement by Day 14 (p = 0.0035), with no further improvement from Day 14 to 28 (p > 0.99). ESGD grades from Day 0 to 28 decreased significantly (95% CI −1.92 to −0.91 grades) (p = 0.0002). Out of the horses (6/23) that had glandular lesions, 5/6 healed over time; however, this was not a significant change (p = 0.75). Injection reactions included oedema, heat and pain at the injection site. Considering the total number of injections across the whole study, 23% of horses experienced an injection site reaction. The number of injection site reactions increased following each dose (8%, 13%, 22% and 48%, respectively). The formulation did not appear to have adverse systemic effects. Serum omeprazole mean Cmax was 46.2 ng/ml (±17.4 ng/ml), and these concentrations maintained at approximately 9.6 ng/ml (±4.6 ng/ml) for 7 days following dosing. This formulation is compounded and has not completed FDA investigation, which may increase formulation variability as it is produced or stored. The lack of control groups and potential bias in lesion grading are additional recognised limitations. The results of this study provide preliminary safety and efficacy data with regard to a novel LAO‐USA formulation. Future study is warranted to describe safety and efficacy for both ESGD and EGGD and would support further FDA investigation.