No Added Benefits from Higher Bute Dosage

Higher dosages of phenylbutazone (Bute) don't make chronically lame horses any sounder than standard doses, according to a study in a recent issue of the Journal of the American Veterinary Medical Association. Thus, giving a lame horse extra Bute gives no benefit, costs more, and carries a higher risk of toxicity and/or gastrointestinal problems.

Ronald S. Erkert, DVM, graduate student of physiological sciences at Oklahoma State University, and other researchers compared the analgesic (painkilling) effects of Bute given intravenously at a dosage of 4 mg/kg/day (2 g) or 8 mg/kg/day (4 g) in nine horses with chronic forelimb lameness due to navicular syndrome. The intravenous (IV) route was chosen because it is "much easier to more accurately dose an animal with an IV product than an oral product,"said Erkert.

Each horse received either 2 or 4 g of Bute or physiologic saline solution (no analgesic) daily for four days. "For the IV product, I feel it is best to give a full dose once daily," said Erkert. "This allows elimination of most of the product from the plasma before the next dose, thus minimizing toxicity."

The horses were evaluated for lameness at six, 12, and 24 hours after the fourth dose was administered by trotting across a force plate to measure mean peak vertical force (mPVF), or how hard the horse's hooves hit the ground when he is moving. Lower forces correspond with more severe lameness as the horse favors the sore limb.

Mean peak vertical forces were significantly increased (the horses were less lame) at six, 12, and 24 hours after both Bute dosage regimens were completed, but with no significant differences in the changes of mPVF between the low and high dosage groups. This suggests that the effects of Bute are not increased with increasing doses and appear to be longer than predicted in previous studies. Erkert said, "If a full dose (2 g) of either IV or oral product does not eliminate the pain completely, administering more will not do so either."

Most owners give their horses oral Bute as opposed to an IV injection to treat pain. Erkert said, "Now that we have the data for the IV products, it would be interesting and valuable to repeat the study using available oral products to see if similar results are found."

About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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