Effect of body weight on the pharmacokinetics of flunixin meglumine in miniature horses and quarter horses

In most species, large variations in body size necessitate dose adjustments based on an allometric function of body weight. Despite the substantial disparity in body size between miniature horses and light-breed horses, there are no studies investigating appropriate dosing of any veterinary drug in miniature horses. The purpose of this study was to determine whether miniature horses should receive a different dosage of flunixin meglumine than that used typically in light-breed horses. A standard dose of flunixin meglumine was administered intravenously to eight horses of each breed, and three-compartmental analysis was used to compare pharmacokinetic parameters between breed groups. The total body clearance of flunixin was 0.97 +/- 0.30mL/min/kg in miniature horses and 1.04 +/- 0.27mL/min/kg in quarter horses. There were no significant differences between miniature horses and quarter horses in total body clearance, the terminal elimination rate, area under the plasma concentration versus time curve, apparent volume of distribution at steady-state or the volume of the central compartment for flunixin (P>0.05). Therefore, flunixin meglumine may be administered to miniature horses at the same dosage as is used in light-breed horses.