Meloxicam vs. Phenylbutazone: Effects on Horses' Gastric Mucosa Studied

While prolonged use of non-steroidal anti-inflammatory (NSAID) drugs has long been associated with gastrointestinal problems in horses, some newer NSAIDs on the market could have fewer adverse effects than older ones.

Non-steroidal anti-inflammatory drugs impair the inflammatory process by inhibiting the enzyme cyclooxygenase (COX), which are responsible for inflammatory responses in the body. There are two 'subtypes' of COX: COX-2 is primarily associated with inflammation while COX-1 is associated with 'house keeping' activities, including protection of the gastric mucosa (lining). While older NSAIDs are nonselective in targeting these enzymes, the newer ones target COX-2 and aim to spare COX-1 enzymes.

Researchers from Charles Sturt University (CSU) in Australia recently evaluated the effects of two NSAIDs (meloxicam, a preferential COX-2 inhibitor, and phenylbutazone (bute), a nonselective inhibitor) on equine gastric mucosa.

Twenty-five light breed horses were assigned to five treatment groups for the two-week study:

  • Group A received a placebo (product vehicle only) orally;
  • Group B received the recommended daily dose of meloxicam (0.6 mg/kg) orally;
  • Group C received three times the recommended daily dose of meloxicam (1.8 mg/kg) orally;
  • Group D received five times the recommended daily dose of meloxicam (3.0 mg/kg) orally; and
  • Group E received phenylbutazone at three different doses orally (Day 1: 4.4 mg/kg twice daily; Days 2-5: 2.2 mg/kg twice daily; Days 6-14: 2.2 mg/kg once daily)

The team performed sucrose (sugar) permeability testing on each horse on Days 0 and 13 and compared these findings to endoscopic gastric ulceration scores assigned by assessors blind to treatment on Days 0, 6, and 13.

Regarding sucrose permeability testing, Sharanne Raidal, BVSc, MVSt, PhD, GradDipEd, FANZCVSc, associate professor at CSU and member of the research team, explained, "If the gastric mucosa is damaged (or 'leaky') then it is likely that some of the sucrose will be absorbed into circulation and can then be measured in blood samples."

Key study results included:

  • No changes were found in Group A and B horses;
  • Some Group C and D horses developed changes associated with NSAID toxicity, including right dorsal colitis, ventral (stomach) edema, loose feces, and loss of appetite;
  • Two horses in Group E developed complications, including sheath edema and right dorsal colitis;
  • Significant increases in sucrose concentrations were found in group E only; and
  • Gastric endoscopy results did not correlate with sucrose permeability testing findings, suggesting that endoscopic evaluation could underestimate both the presence and severity of gastric ulcers.

"Our findings suggest that selective COX inhibitors may have a lesser effect on gastric mucosal integrity than nonselective agents," the team reported.

The study, "Effects of Meloxicam and Phenylbutazone on Equine Gastric Mucosal Permeability," was published in the November-December 2012 issue of Journal of Veterinary Internal Medicine.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.