Pharmacokinetics of furosemide administered 4 and 24 hours prior to high‐speed exercise in horses

Abstract

Furosemide is a diuretic agent used commonly in racehorses to attenuate the bleeding associated with exercise-induced pulmonary hemorrhage (EIPH). The current study describes serum and urine concentrations and the pharmacokinetics of furosemide following administration at 4 and 24hrs prior to maximal exercise. Eight exercised adult Thoroughbred horses received a single IV administration of 250mg of furosemide at 4 and 24hrs prior to maximal exercise on a high-speed treadmill. Blood and urine samples were collected at time 0 and at various times for up to 72hrs and furosemide concentrations determined using liquid chromatography-tandem mass spectrometry. Serum furosemide concentrations remained above the LOQ (0.05ng/ml) for 36hrs in 3/8 and 1/8 horses in the 4- and 24-hrs groups, respectively. Serum concentration data were best fit by a two-compartment model. There was not a significant difference in the volume of distribution at steady-state (0.594±0.178 [4hrs] and 0.648±0.147 [24hrs] L/kg) or systemic clearance (0.541±0.094 [4hrs] and 0.617±0.114 [24hrs] L/hrs/kg) between horses that were exercised at 4- and 24hrs postdrug administration. The mean±SD elimination half-life was 3.12±0.387 and 3.23±0.407hrs following administration at 4 and 24hrs prior to exercise, respectively.