Pharmacokinetic and pharmacodynamic effects of 2 registered omeprazole preparations and varying dose rates in horses.
Authors: Wise Jessica C, Hughes Kristopher J, Edwards Scott, Jacobson Glenn A, Narkowicz Christian K, Raidal Sharanne L
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Omeprazole Preparations and Dosing in Horses Two registered omeprazole formulations—a traditional enteric-coated paste and a newer in-feed granule preparation—were compared across bioavailability, dose titration, and gastric pH studies in twelve sound mares to determine whether these products deliver equivalent clinical effects despite differences in plasma drug concentrations. The novel granule formulation achieved substantially higher peak plasma concentrations (median 1032 ng/mL versus 283 ng/mL) and area-under-curve values following single-dose administration, though absolute oral bioavailability was comparable between products (55% and 17% respectively, not significantly different). Both preparations reduced gastric squamous ulcer scores and elevated gastric fluid pH similarly, with near-bioequivalence in pharmacodynamic outcomes except for percentage of time pH remained below 4—demonstrating a critical disconnect between plasma omeprazole levels and actual gastric acid suppression in equine patients. These findings challenge the assumption that higher circulating drug concentrations necessarily translate to superior clinical outcomes, suggesting practitioners can confidently substitute the in-feed formulation as an alternative whilst recognising that standard dosing protocols may require recalibration to account for individual variation in bioavailability, which ranged from 15–88% across horses receiving identical doses.
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Practical Takeaways
- •The novel in-feed omeprazole granule formulation appears clinically equivalent to the reference paste for ulcer healing and gastric pH control, offering practitioners an alternative delivery option
- •Higher plasma concentrations from the new formulation do not translate to better gastric protection, supporting the use of either product based on horse management practicality rather than dose considerations
- •When selecting omeprazole products for gastric ulcer management in horses, focus on compliance and ease of administration rather than assuming higher plasma levels equal better clinical outcomes
Key Findings
- •Novel in-feed omeprazole granules (NOV) achieved higher peak plasma concentration (Cmax 1032 ng/mL) and greater AUC than reference paste (282.7 ng/mL) despite similar absolute bioavailability (~55% vs 17%, P=0.25)
- •Both omeprazole preparations reduced gastric squamous ulcer scores and increased gastric fluid pH with bioequivalence for most pharmacodynamic measures except % time pH <4
- •Plasma omeprazole concentrations and dose rates do not reliably predict pharmacodynamic outcomes in horses, suggesting clinical efficacy is independent of plasma levels