At the 2021 American Association of Equine Practitioners’ Convention in Nashville, Tennessee, Rebecca Bishop, DVM, of the University of Illinois reported on a study about the effects of NSAIDs on equine colon health. She noted that 42% of horses are prescribed at least one NSAID for various issues, making it a ubiquitous medication in the horse world. Many NSAIDs—such as phenylbutazone and flunixin meglumine—are non-specific at the level of COX-2 and COX-1 inflammatory pathways, with the potential to elicit gastric, colonic or renal injury.
The study compared the use of COX-2-specific firocoxib to flunixin in 12 healthy horses with normal physical exams, normal complete blood counts and normal serum chemistries. The horses all received the same treatments with a 6-month washout in between administrations. In addition to the NSAIDs received in each treatment course, each horse was administered omeprazole 1 mg/kg orally for 5 days.
- Treatment 1 = flunixin 1.1 mg/kg IV every 12 hours for five days.
- Treatment 2 = firocoxib 0.3 mg/kg orally once, then 0.1 mg/kg oral once daily for four days.
Blood samples were taken before and after the five-day treatment period. Transabdominal ultrasound was used to grade edema in the colon as well as colon thickness. All horses had similar ultrasound findings prior to treatment.
Despite concurrent omeprazole treatment, there was a significant difference of subclinical colon inflammation with increasing colon edema and thickness from firocoxib treatment but not with flunixin. Total protein increased following firocoxib but decreased with flunixin. (Usually, total protein decreases are associated with colonic inflammation and protein-losing enteropathy.) No differences in PCV were noted, so the elevation in total protein with firocoxib is not attributable to hydration status.
Both groups experienced a significant increase in creatinine, possibly due to subclinical kidney injury, although the BUN did not change over time in either treatment group. In general, there were no clinically significant changes in other biochemistry parameters, and all remained within normal limits.
It is notable that a recent study identified an increased incidence of lower intestinal complications with impaction and colic signs when phenylbutazone and omeprazole were administered concurrently, so this might have had some effect on the results.
Another possible consideration expressed by Bishop was that orally-administered firocoxib could elicit an altered effect on the medicine in the lower intestines. She also pointed out that this study was restricted to healthy horses and more studies are necessary to look at treatment of horses with disease conditions.