Impact of concurrent treatment with omeprazole on phenylbutazone-induced equine gastric ulcer syndrome (EGUS)

BACKGROUND: Phenylbutazone is commonly prescribed for treatment of various painful or inflammatory disorders in horses, but is associated with gastrointestinal (GI) adverse effects. Anecdotally, many practitioners prescribe omeprazole concurrently with phenylbutazone to reduce development of equine gastric ulcer syndrome (EGUS), but the efficacy and safety of this practice remains unknown. OBJECTIVES: To evaluate the effect of omeprazole on phenylbutazone-induced equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD). STUDY DESIGN: Randomised block experimental design. METHODS: Twenty-two horses with EGGD and ESGD scores ≤2 were included. Horses were assigned to treatment groups: phenylbutazone (4.4 mg/kg PO q 12 h; PBZ), phenylbutazone plus omeprazole (4 mg/kg PO q. 24 h; PBZ/OME) or placebo (CON) in a randomised block design based upon initial EGGD score. Horses were treated for up to 14 days. Gastroscopy was performed weekly; CBC and biochemistry were performed at Day 0 and study end. Horses were monitored for signs of colic and/or diarrhoea. RESULTS: EGGD score increased in PBZ (median change 1, inter-quartile range, [IQR], 0-2) compared to PBZ/OME (median change 0, IQR -1 to 0; P = .05). PBZ/OME (6/8) had more intestinal complications than CON (0/6; difference between proportions = 75%; 95% CI, 23%-93%; P = .03). Plasma protein concentrations decreased in PBZ, compared to CON (mean difference between groups, 14 g/L; 95% CI, 1.04-27; P = .03). Five horses were withdrawn from the study due to intestinal complications (n = 3 PBZ/OME and n = 2 PBZ); one horse (PBZ) was withdrawn due to severe grade 4 EGGD. MAIN LIMITATIONS: Small sample size and changes in management for the 2-3 days prior to study initiation; variable treatment duration among groups due to development of complications. CONCLUSIONS: Administration of omeprazole ameliorated PBZ-induced EGGD, but was associated with an increase in intestinal complications. Caution should be exercised when co-prescribing NSAIDs and omeprazole in horses, particularly in association with change in management