Researchers recently confirmed concerns about negative effects of a popular long-term nonsteroidal anti-inflammatory (NSAID) treatment might be overstated. Horses receiving firocoxib had essentially normal bloodwork even after years of medication, meaning the drug didn’t appear to harm the kidneys, suppress the immune system, or cause protein loss. The findings suggest firocoxib might be safe even well beyond the labeled 14-day use, said Langdon Fielding, DVM, MBA, Dipl. ACVECC, ACVSMR, of Loomis Basin Equine Medical Center, in Penryn, California.

“This is good news for horse owners,” Fielding said. “It’s nice to know that this medication can be used long-term without significant changes in laboratory values.”

Firocoxib for Chronic Pain in Horses

When horses develop chronic pain and inflammation due to injuries, osteoarthritis, or similar disease processes, veterinarians prescribe NSAIDs such as firocoxib (specifically classified as a cyclooxygenase-2 inhibitor). But despite those advantages, Fielding said owners might stop firocoxib after two weeks to avoid potential side effects from extensive use, such as gastrointestinal ulcers and kidney damage. Currently, the drug label calls for once-daily use for up to 14 days in horses, even though similar drugs are used longer in dogs and people with few negative effects, Fielding said.

Those concerns don’t match what Fielding and his colleague Iuri Buzelato Carli, DVM, a resident in equine internal medicine at the University of California, Davis, said they have seen in the field, though.

“There are so many horses using this medication now, so we really wanted some evidence to guide our medical decisions,” Fielding said. “Whenever we see a question that needs to be answered with clinical research, we try to see if we have the data that can be used.”

Studying the Effects of Long-Term Firocoxib Use in Horses

He and Carli ran bloodwork on 232 horses—primarily Quarter Horses, Paints, Arabians, and Thoroughbreds—during a routine wellness program for their patients. Of those, 153 horses averaging 15 years of age (ranging from 1 to 33 years old), had never received firocoxib treatment.

The other 79 horses, averaging 19 years of age (ranging from 5 to 33 years old), had been receiving daily firocoxib at a dose of about 0.13 milligrams per kilogram orally anywhere from two months to nearly four and a half years. Two-fifths of the patients had been on the NSAID for more than a year, and 50% of those had been on it for more than two years. More than half were being treated for osteoarthritis, with the others receiving the medication for laminitis, orthopedic soft tissue injuries such as torn tendons or ligaments, navicular disease, other chronic lameness, or a variety of issues unrelated to lameness.

Comparing the bloodwork results, the team found no clinically significant differences in creatinine, blood urea nitrogen (BUN), or other markers of concern between the two groups, Fielding said.

The firocoxib group—which had been on the drug for an average of 10 months—did have slightly elevated total protein and sodium levels as well as slightly lower white blood cell (WBC) counts. Even so, none of these differences had significant clinical value, he said. How long the horse had been taking the drug didn’t affect lab values either, he said.

Given their experience in practice, the researchers said the findings came as no surprise. “We use this medication a lot, and we have not seen many problems,” Fielding said. “We just needed a more formal analysis to support this belief.”

Take-Home Message

Veterinarians often prescribe firocoxib to manage chronic pain and inflammation in horses, and its long-term use appears safe based on bloodwork. While manufacturers have labeled the drug for once-daily use for up to 14 days, researchers on this study suggest firocoxib might be suitable for extended treatment in appropriate cases. Still, veterinarians should evaluate horses individually and continue to monitor for adverse effects during long-term NSAID therapy.

The study, “Long-Term Firocoxib Use in Horses,” appeared in the Journal of Veterinary Internal Medicine in May 2025.