Is using omeprazole for the prevention of gastric ulcers while treating horses with phenylbutazone (bute) best practice?
Recent research indicates perhaps not.
Prescribing omeprazole alongside treatment with phenylbutazone has become common to reduce the negative impact the pain medication is thought to have on gut health and development of gastric and colonic ulcers.
A recent study, published in the Equine Veterinary Journal by the team at Louisiana State University set out to evaluate the effect of omeprazole on phenylbutazone-induced gastric ulcers, including squamous and glandular ulcers.
Their major findings were:
- Horses treated with a combination of phenylbutazone in combination with omeprazole had more intestinal complications, many of them severe, some resulting in death or horses having to be euthanised.
- Omeprazole treatment was effective in preventing the worsening of phenylbutazone induced glandular ulcers.
- Sudden changes in management should be avoided during treatment with phenylbutazone and in combination with omeprazole.
The take home message?
The use of these two drugs together needs to be carefully considered as it is not universally safe to do so. If you can avoid using both at the same time and use other ways of supporting gut health while horses are on bute, then you probably should.
If you love the details like we do, keep reading!
The Study
Twenty-two horses from the universities teaching herd were enrolled in the study based on inclusion criteria of >3 years old, with squamous and glandular ulcer scores less than 2 and no signs of systemic disease.
Horses were acclimatised 2-3 days prior to initial gastroscope. Prior to this, the horses were fed a diet containing pasture, mixed grass hay and 1kg of pelleted feed (starch max. 17%).
During the study period, horses were individually stalled and fed a diet consisting of mixed grass hay and 1kg grain-based feed (starch max. 33%). Grain based feed was changed from 1kg Purina Omolene 100 to 0.5kg Omolene and 0.5kg Purina Strategy (starch max. 10%) daily after the first cohort due to observations of colic signs.
Horses were allocated into one of three groups (randomised block design based on initial glandular score) and treated for 7-14 days with one of three treatments:
Treatment 1. phenylbutazone paste 4.4mg/kg orally every 12 hours
Treatment 2. phenylbutazone paste 4.4mg/kg orally every 12 hours + omeprazole 4mg/kg orally every 24 hours
Treatment 3. placebo (control) of corn syrup 10ml orally every 12 hours.
There were four cohorts due to stall availability.
Horses were fed two biscuits of hay at 4pm in the evening alongside feed and no hay was present at time of medication administration in the morning. Omeprazole was administered first the following morning, followed by phenylbutazone 30 minutes later, followed by hay and feed.
On day 0, 7 and 14, following 16-18 hours fast, gastroscope was performed by an investigator blinded to treatment. Signs of colic and diarrhoea were observed and recorded throughout the study period.
Gastric fluid and blood was collected on day 0 and day 14 (unless withdrawn earlier). Horses were withdrawn from the study if adverse effects (colic, lethargy, diarrhoea) were identified that required medical intervention or if glandular or squamous ulcers grade 4 was observed.
Due to adverse effects seen in treatment groups in the first cohorts, the last study cohort underwent treatment for 7 days only.
The Results
The results from this study are quite complex due to the complications within treatment groups and as a result, horses being withdrawn from the study but here are the main findings.
Gastric Ulcers
No effect of treatment on squamous ulcers was seen. Glandular ulcers increased by one score in the phenylbutazone group compared with no significant change in the phenylbutazone + omeprazole group.
Interestingly, no obvious change in glandular ulcer scores was seen in the control group however a trend towards increasing squamous ulcer scores which may indicate the role diet and management may play in squamous ulcer formation.
This was also seen in the phenylbutazone group but not in the phenylbutazone + omeprazole group. One horse in the control group appeared not to cope with changes in management with increase of glandular and squamous ulcer scores from 1 to 4 in just 7 days.
Intestinal Complications
Intestinal complication was observed in both treatment groups. These included two out of a total of seven in the phenylbutazone group (including large colon impaction and small colon impaction).
And six out of eight in the phenylbutazone + omeprazole group (including large colon impaction, small colon impaction, colic of undetermined cause, diarrhoea, colitis and secondary sepsis resulting in death and ulcerative colitis with septic peritonitis leading to euthanasia).
No horses in the control group developed complications.
Study Limitations
The authors acknowledge that a high dose of phenylbutazone was used (4.4mg/kg twice daily) however justified that this dose is occasionally used in clinical practice. Lower doses of phenylbutazone (2.2mg/kg twice daily) are generally recommended.
Sudden changes (2-3 days adaption) in dietary and housing management were also confounding factors however not dissimilar to clinical practice where horses may be brought in off pasture and hospitalised or stalled due to an injury.
Previous studies have shown changes in diet alter intestinal microbiome in horses and both dietary and housing management changes have been associated with colic. Therefore, this may have predisposed horses in the treatment groups to intestinal complications.
BUT it was not the determining factor as no complications were observed in the control group.
Summary
Care must be taken when treating horses with omeprazole alongside phenylbutazone.
The exact cause of complications in treatment groups is unclear however the authors of this study suggest changes to microbial populations in the gut, altered gut motility and intestinal inflammation may have all contributed.
Talk to your veterinarian about any concerns prior to starting these medications, particularly if you are using both at once.
Importantly, try to minimise changes in management practices at the same time especially if you are introducing grain-based feed.
If your horse requires pain relief in the form of phenylbutazone, investigate alternatives to omeprazole that support gut health through other actions e.g. marine source calcium to buffer gastric acid, pectin or lecithin to protect the stomach lining and supplying the amino acids, glutamine and threonine, which help repair and protect the gut mucosa.
Plus be sure to reduce stress as stress is one of the biggest predisposing factors for glandular ulceration.
And if you really, REALLY like the details, here is the full article:
Ricord M, Andrews FM, Yñiguez FJM, et al. Impact of concurrent treatment with omeprazole on phenylbutazone-induced equine gastric ulcer syndrome (EGUS). Equine Vet J. 2021;53:356–363. https://doi.org/10.1111/evj.13323
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