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Pharmacological particulars
ATCvet code: QC03CA01
Pharmacological properties
Pharmacotherapeutic group
Cardiovascular system, high-ceiling diuretics, sulfonamides, plain; furosemide.
Pharmacodynamic properties
Furosemide is a derivative of sulphamoyl-anthranilic acid and is a rapid onset diuretic used in animals and humans. Furosemide acts on the urine producing regions of the nephron and increases the filtration volume while impairing the re-absorption of sodium, chlorine and water. An isotonic or slightly hypotonic urine with unchanged or slightly acid Ph is produced. Potassium excretion is only significantly increased after large doses.
Pharmacokinetic particulars
Cattle
The absorption of furosemide is rapid but incomplete with maximum plasma levels occurring within 1 hour of dosing depending on the administration route. Furosemide is not accumulated after repeated dosing as evidenced by comparison of plasma profiles and of tissues concentrations.
The volume of distribution is relatively low, indicating limited distribution into tissues (mainly liver and kidney), also reflecting the extensive plasma protein binding. Absorption and tissue distribution are extremely fast in cattle after i.m. administration. In plasma, maximum levels range from 15 minutes to 1.5 hour, and the half-life is 0.22-2.7 hours. Elimination is predominantly renal via urine, and is clearly prolonged after oral and i.m. administration compared to i.v. administration (probably because delayed absorption). Lesser quantities are eliminated via faeces and very little via milk (half-life 3 hours). Only small quantities are excreted in the bile. The majority of the total dose is excreted within 24 hours.
Horse
The apparent volume of distribution is 0.66 L/kg in horses. The elimination half-life is prolonged after i.m. administration compared with i.v. administration (65-86 vs 25-39 minutes, respectively), probably on account of delayed absorption. The half-life of 7.6 hours from the urine points to a distribution to poorly perfused tissues. The total clearance is about 12 mL/kg/min and the renal excretion accounts for 60% in unmetabolised form. Plasma protein binding of furosemide in horses in about 95%. Up to 60% of the amount of furosemide injected i.v. is rapidly excreted unchanged in the urine, and furosemide is still detectable in urine for about 12 hours.
Dog and cat
Following parenteral administration, furosemide is rapidly absorbed with maximum plasma levels occurring within 10-15 minutes. It is not accumulated after repeated dosing. Plasma half-lives are similar across species after i.v. administration (dog 12-24 minutes). Elimination is rapid and predominantly via the kidneys in the urine. The majority of the total dose is excreted within the first 24 hours (after i.v. injection in dogs, about 44-56% of the dose are excreted in the urine within one hour and 55-69% within 24 hours). The faeces contain 17-39% of the dose. Plasma protein binding of furosemide is 91% and estimated distribution volume is 0,52 L/kg. Furosemide metabolizes in very small amounts (main metabolite: 4-chloro-5-sulfamoyl-anthranilic-acid, no diuretic activity).