Abstract
The diuretic effect and fate of furosemide were investigated in horses by collecting urine samples from the bladder via an indwelling balloon catheter. The plasma and urinary furose mide concentrations were determined by high-performance liquid chromatography (HPLC) with spectrofluorometric detection. The results obtained were as follows. 1) The balloon catheter method was very available for collecting accurately complete urine samples at each designated time-period after furosemide administration. 2) After furosemide administration the urinary flow increased markedly and reached a peak at 20 min. The furosemide-induced diuretic response was dose-dependent and the intramu scular route was more effective than intravenous administration. 3) The plasma con centration-time curves obtained after intravenous administration of furosemide were fitted to a 2-compartment open model with a phase half-lives of 6, 3 and 5, 9 min and 9 phase half-lives of 59, 4 and 60.8 min after doses of 0, 5 and 1.0 mg/kg, respectively. After intra muscular administration, the peak plasma furosemide concentration was reached at 10 min. 4) Irrespective of the dose and route of administration, the urinary concentration of furosemide showed a characteristic change and shifted from decreasing to increasing at 1 h after administration. Over 60% of the administered dose was excreted in the urine as unchanged furosemide during the 6 h subsequent to administration. 5) The furosemide induced diuretic response was related linearly to the furosemide plasma concentration and urinary excretion rate.
