THE PHARMACOKINETICS OF FUROSEMIDE IN ANESTHETIZED HORSES AFTER BILATERAL URETERAL LIGATION

The pharmacokinetics of furosemide were investigated in anaesthetized horses with bilateral ureteral ligation (BUL) with (n = 5) or without (n = 5) premedication with phenylbutazone. Horses were administered an int-ravenous (i.v.) bolus dose of furosemide (1 mg/kg) approximate to 60-90 min after BUL. Plasma samples collected up to 3 h after drug ad ministration were analysed by a validated high performance liquid chro matography method. Median plasma clearance (CL,) of furosemide in anae sthetized horses with BUL was 1.4 mL/ min/kg. Apparent steady state vo lume of distribution (Vd(ss)) ranged from 169 to 880 mL/kg and the eli mination half life (t(1/2)) ranged from 83 min to 209 h. No difference s in plasma concentration or kinetic parameter estimates were observed when phenylbutazone was administered before furosemide administration . BUL markedly reduces the elimination of furosemide in horses and mod els the potential effects that severe changes in kidney function may h ave on drug kinetics in horses.