Like humans, horses spike fevers. But while physicians can recommend acetaminophen and ibuprofen for patients with pyrexia (fever) who are suffering from discomfort, there are currently no medications labeled to control it in horses. So equine practitioners generally administer non-steroidal anti-inflammatory (NSAID) drugs in pyrexic animals.

The NSAID dipyrone is approved in several different countries—but not the United States–for use in animals and people to reduce fever and relieve pain. Emily Sundman, DVM, of Kindred Biosciences Inc., in Burlingame, California, lead a study to investigate this drug’s safety and efficacy in horses. She summarized the results at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.

“Currently, no medication is approved by the FDA to control fever in horses, which is a challenge for veterinarians treating these horses,” Sundman explained. “Controlling fever in horses has many positive outcomes, including maintaining appetite and water consumption, and promoting normal locomotion and behaviors that quicken recovery.”

With the owners’ consent, Sundman and colleagues studied horses of various breeds from 14 clinical research sites in 12 states. The horses had a fever of at least 102°F, and to be included in the study, they had to be older than 1 year, not pregnant, and free of severe systemic disease. The causes of fever varied, including respiratory infection, tick-borne illness, immune-mediated problems, and gastrointestinal issues.

The researchers randomly assigned horses to one of two groups: the treatment group that received 30 mg/kg of intravenous dipyrone or the controls that received a placebo. Researchers were blinded to the groups. They recorded horses’ temperatures six hours after treatment; if a subject’s fever was not under control, they removed it from the study. They considered treatment to be effective if body temperature decreased by 2°F or the horse’s body temperature returned to normal. Dipyrone was effective in 77% of horses treated, said Sundman.

In the same study, Sundman investigated the drug’s field safety. Treated horses received additional doses of 30 mg/kg of dipyrone up to three times daily, under their veterinarian’s direction. The team completed a physical exam and bloodwork when each horse exited the study.

Post-treatment adverse reactions were mild, occurred at similar rates among the placebo and dipyrone groups, and did not appear to be clinically problematic. These included injection site reactions, loose stool, and loss of appetite, with the

latter two signs generally related to the fevers. Bloodwork abnormalities were consistent with horses suffering from fever and could have been related to the underlying cause of disease.

In conclusion, dipyrone was effective for controlling fever in horses when given at an intravenous dose of 30 mg/kg, said Sundman. Few adverse events were reported, and most of those were mild. Horses appeared to tolerate dipyrone well, she added.

She said Kindred Biosciences hopes to gain FDA approval for dipyrone for use in horses.