Flunixin Meglumine Doses: More or Less? (AAEP 2012)

Veterinarians use non-steroidal anti-inflammatory drugs (NSAIDs) to manage equine pain in a variety of situations. Foot pain can often be difficult to control, so Jonathan Foreman, DVM, MS, Dipl. ACVIM, of the University of Illinois at Urbana-Champaign, and his colleagues examined the possibility that higher-than-standard doses might better alleviate foot pain. He presented his team's results at the 2012 American Association of Equine Practitioners' (AAEP) Convention, held Dec. 1-5 in Anaheim, Calif.

He and his colleagues used a reversible model of equine foot lameness to test this idea--a reversible heart bar shoe can make sound horses lame temporarily, and the pain is abated completely when researchers loosen the screw in the shoe to relieve foot pressure. This model allowed the researchers to study the same horses weekly for four weeks so that each horse served as its own control. The more the researchers tighten the screw in the shoe, the higher the pain level as reflected by increasing heart rates. They confirmed the effects of the tightened shoe in each horse with a palmar digital (heel) nerve block. The horses' heart rates dropped from 60 to 40 beats per minute (bpm) following this regional anesthesia application.

Foreman wanted to see if the half-strength dose of flunixin commonly used as an anti-endotoxin dose in colic treatment could provide sufficient relief for foot pain. In a previous study he compared varying doses of phenylbutazone (Bute) and found no difference between the effects of a normal, single dose (1x), and those of twice the normal dose (2x), but the effects of one-half dose were not as long-lived as those seen with a 1x dose of phenylbutazone.

In this study the scientists compared the effects of varying intravenous doses (half-dose, 1x, 2x) of flunixin meglumine; they used saline as a control. Ten sound horses wore a reversible heart bar shoe on the left front foot. Following treatment, the 1x and 2x doses improved heart rates for the 12-hour duration, whereas heart rates remained elevated in the control horses. Heart rates in the horses given half-doses of flunixin did not decrease as much as those in the 1x and 2x horses, and they didn't remain low for as long. "They responded intermittently and not as obviously," Foreman commented. There was no difference in heart rate results between the horses receiving 1x or 2x flunixin meglumine.

Plasma concentrations of flunixin meglumine increased in a dose-dependent manner, but by Hour 8, there was no difference among concentrations at half-dose, 1x, and 2x doses. This indicates that horses rapidly metabolize and excrete the drug.

In conclusion, Foreman noted that the double dose was no more effective than the single dose and presents a higher risk of toxicity. The half-dose was less effective than the single dose; therefore, one can't rely on an anti-endotoxic half-dose to provide complete pain control for horses with painful hoof conditions such as laminitis. This is significant when treating colicking horses with smaller doses of flunixin meglumine to alleviate intestinal pain and combat endotoxemia. Since laminitis can also be a sequel to colic, owners and veterinarians should not rely on smaller-than-usual doses of flunixin meglumine to alleviate musculoskeletal pain. Foreman summed the study up by saying, "More is not better and less is less effective."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.