Evaluation of the effects of medium-term (57-day) omeprazole administration and of omeprazole discontinuation on serum gastrin and serum chromogranin A concentrations in the horse.
Authors: Clark Bethanie, Steel Catherine, Vokes Jessica, Shan Jack R, Gedye Kristene, Lovett Amy, Sykes B W
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Rebound hyperacidity following omeprazole withdrawal has been hypothesised as a mechanism driving rapid recurrence of squamous gastric ulceration in racehorses, potentially mediated by elevated gastrin levels triggering increased acid secretion. Researchers administered 2.28 g omeprazole daily for 57 days to 14 Thoroughbreds in training, measuring serum gastrin and chromogranin A (a marker of neuroendocrine response) at baseline, weekly during treatment, and for five weeks post-discontinuation using radioimmunoassay and ELISA respectively. Serum gastrin rose 2.5-fold within the first week of treatment but plateaued thereafter, crucially returning to baseline concentrations within 2–4 days of stopping omeprazole—a timeframe considerably shorter than the months typically required for ulcer recurrence. Chromogranin A showed no meaningful changes in response to either treatment or cessation, suggesting the proposed rebound hyperacidity mechanism may not operate through sustained neuroendocrine activation. These findings challenge current tapering protocols; the rapid normalisation of gastrin indicates abrupt omeprazole cessation poses minimal biochemical risk of acid rebound, implying that ulcer recurrence is more likely driven by other factors such as dietary management, training intensity, or behavioural stress rather than pharmacologically-mediated acid hypersecretion.
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Practical Takeaways
- •Omeprazole causes rapid gastrin elevation within the first week but reaches a plateau thereafter, so the rebound hyperacidity seen clinically may not be purely gastrin-mediated
- •Gastrin levels normalize quickly after stopping omeprazole (2-4 days), suggesting tapering schedules are unnecessary and may not prevent ESGD recurrence
- •The rapid return to baseline gastrin after treatment cessation indicates alternative mechanisms may be responsible for ESGD recurrence in horses—focus management strategies on other factors
Key Findings
- •Serum gastrin concentrations increased 2.5-fold from baseline by day 7 of omeprazole treatment (P < 0.001) but did not increase further during the 57-day treatment period
- •Serum gastrin concentrations returned to baseline within 2-4 days after discontinuation of omeprazole
- •No significant changes in serum chromogranin A concentrations were observed in response to treatment or discontinuation
- •Results do not support the use of tapering protocols for omeprazole discontinuation in horses