Adding Acetaminophen to Lameness Management Plan for Horses

Acetaminophen appears both safe and effective in horses with naturally occurring lameness, making it another potential treatment option for horses with musculoskeletal discomfort.

Traditional means of controlling pain caused by chronic musculoskeletal injuries include nonsteroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone or “bute.” While NSAIDs are effective, they are associated with side effects when used either at high doses or with long-term administration. Side effects include kidney damage as well as gastric ulceration due to cyclooxygenase-1 (COX-1) inhibition.

“A multimodal treatment approach to managing chronic lameness in horses should be implemented when possible. NSAIDs can be used sparingly while still ensuring the horse can move comfortably,” explained Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist.

“A multimodal treatment plan may include the prescription medications tramadol and gabapentin. Certain nutritional supplements may also be included, such as glucosamine, chondroitin sulfate, and hyaluronic acid, as well as DHA and EPA found in marine-based omega-3 supplements that reduce inflammation.”

Another medication that might be useful for full-spectrum musculoskeletal pain management is acetaminophen. While also considered an NSAID, acetaminophen’s main pain-relieving mechanism differs from traditional NSAIDs like phenylbutazone. Specifically, it does not block COX-1.

In human medicine, acetaminophen is often combined with traditional NSAIDs to provide pain relief without the concern for added side effects associated with NSAID administration.

“Acetaminophen is currently used sparingly in equine practice, and few data exist supporting its efficacy in horses with naturally occurring lameness,” Crandell said.

Virginia-based veterinarians put together a research trial involving acetaminophen.^* They recruited 12 lame but otherwise healthy horses that were part of a teaching herd and used for riding. The degree of lameness was considered moderate, ranging from 2 to 4 out of 5 on the five-point AAEP lameness scale. Sources of lameness were attributable to conditions such as osteoarthritis, navicular syndrome, chronic flexor tendonitis, and various ligament injuries.

Horses were administered 30 mg/kg of over-the-counter acetaminophen by mouth twice daily for 21 days. Lameness examinations were performed on day 21 at 1, 2, 4, 8, and 12 hours after the final dose of acetaminophen and again on day 35, 14 days after the final acetaminophen dose. Both subjective (visual) lameness examinations using the five-point AAEP lameness scale as well as objective lameness evaluation using body-mounted inertial sensors were performed.

Lameness transiently improved in horses based on both the subjective and objective lameness evaluations. Further, clinical data, including blood work, liver biopsies, and endoscopy exams of the stomach lining, remained within normal limits and was not significantly changed after treatment.

“Together, these data suggest that acetaminophen is both safe and effective in horses with naturally occurring lameness. However, because the improvement in lameness was only transient, acetaminophen may not be suitable as monotherapy for controlling discomfort from musculoskeletal disease,” Crandell said.

Thus, other therapies such as NSAIDs and joint supplements should also be used with acetaminophen for a more robust approach to pain management in lame horses. Each patient’s pain management plan, however, should be curated under veterinary guidance.

 ^*Mercer M.A., J.L. Davis, H.C. McKenzie, C.R. Byron, M.E. Kelleher, L. Trager, T.E. Cecere, K.E. Wilson, R.M. Council-Troche, and S.R. Were. 2024. Pharmacokinetics, clinical efficacy and safety of acetaminophen (paracetamol) in adult horses with naturally occurring chronic lameness. Equine Veterinary Journal 56(1)202-214.