THE PHARMACOLOGY OF FUROSEMIDE IN THE HORSE .5. PHARMACOKINETICS AND BLOOD-LEVELS OF FUROSEMIDE AFTER INTRAVENOUS ADMINISTRATION

Abstract

Blood levels of furosemide [a diuretic drug] in horses were determined after 0.5- and 1.0 mg/kg doses administered i.v. Analyses indicated that the pharmacokinetic parameters were dose independent and best described by a 3-compartment open model. The .alpha.-, .beta.- and .gamma.-phase half-lives of 5.6, 22.3 and 158.5 min, respectively, were observed after the 0.5-mg/kg dose. The respective half-lives after the 1.0-mg/kg dose were 5.8, 24.1 and 177.2 min. After a 0.5-mg/kg dose of furosemide, population frequency distributions were evaluated at 1 h and 4 h post-drug administration. At 1 h after dosing, the blood levels of furosemide in 30 horses were normally distributed. The mean plasma level was 97.9 ng/ml with a range of 41.9 ng/ml-155.8 ng/ml and a SD of 25.0 ng/ml. Analyses of blood levels of furosemide in 47 horses at 4 h after drug administration indicated that the population distribution was better fit by a normal curve after log transformation of the values. The mean plasma level at 4 h post-dosing was 9.6 ng/ml with a range of 4.0 ng/ml-19.4 ng/ml and a SD of 3.1 ng/ml. Based on this population distribution of the plasma levels, the probability of finding furosemide plasma concentrations above 24.6 ng/ml at 4 h after anti-epistaxis dose was estimated at less than 1 in 1000.