Phenylbutazone, or more commonly known in the equine community as ‘bute’, is a non-steroidal anti-inflammatory drug (NSAID) for the short-term treatment of pain, inflammation and fevers. Bute for horses is prescribed by veterinarians for lameness, resulting from soft tissue injury, muscle soreness, bone and joint problems and laminitis.
Phenylbutazone binds strongly to proteins in a horse’s blood plasma and begins circulating (Bogan, 1972). It works to reduce inflammation by blocking the effects of prostaglandins, a large group of hormones that act on the body in many ways, including mediating the inflammatory response. Bute primarily inhibits an enzyme called cyclooxygenase (COX). Cyclooxygenase enzymes metabolize arachidonic acid (a component of the cellular wall) into molecules called eicosanoids. Eicosanoids include prostaglandin molecules. By inhibiting COX enzymes from metabolizing prostaglandins, bute reduces the body’s ability to produce inflammation (Banse et al, 2017). The reduction in inflammation aids in the recovery process and the relief from pain allows the horse to be more comfortable while they are recovering.
While bute for horses controls the prostaglandins released by the damaged tissue, it also acts on prostaglandins produced by normal tissue. These prostaglandins have ‘normal’ housekeeping functions in the body; they regulate blood flow to the kidneys and the lining of the gastrointestinal tract, and mucus production in the stomach (Banse et al, 2017). Overuse or incorrectly administering bute leads to kidney damage and gastrointestinal ulcers.
At a minimum, all horse owners should consult with their vet before administering bute. Depending on your horse’s situation, your vet may need to examine your horse, they may prescribe a different treatment, or they may provide you with careful guidelines to follow when administering bute.
Bogan, J. (1972) The determination of phenylbutazone in horse plasma. Vet. Record. 90, 199.
Banse, H., Cribb, A. (2017) Comparative Efficacy of Oral Meloxicam and Phenylbutazone in Experimental Pain Models in the Horse. Can Vet J. 58, 157-167