Effect of age and training status on pharmacokinetics of flunixin meglumine in Thoroughbreds

Abstract

SUMMARY The effect of age and training status on the pharmacokinetics of flunixin meglumine was evaluated in 16 Thoroughbreds. Horses were assigned to 1 of 3 groups on the basis of age and training status: group A (n = 6), horses in active training and ≤ 5 years old; group B (n = 5), horses out of training for a minimum of 6 weeks and ≤ 5 years old; and group C (n = 5), horses out of training for at least 2 years and ≥ 9 years old. After administration of 500 mg of flunixin meglumine iv, multiple serum and urine samples were obtained over 24 hours and assayed for flunixin by high-performance liquid chromatography. Although the mean distribution rate constant and volume of distribution were similar for the 3 groups, mean total body clearance and elimination rate constant were significantly (P < 0.05) greater and half-life significantly (P < 0.01) less in groups A and B, compared with group C. Differences in pharmacokinetic values were not observed between the horses in groups A and B. In addition, the changes in clearance, elimination rate constant, and half-life of flunixin were found to significantly (P < 0.05) correlate with age. The results of this investigation indicated that age, but not training status, influences disposition of flunixin meglumine in Thoroughbreds.