Biotransformation of furosemide in patients with acute pulmonary edema

Furosemide (20-80 mg) was administered iv over 5 min to 16 patients with the diagnosis of acute pulmonary edema due to left heart failure. Serum and urine samples collected during the 24 hr after administration were assayed for furosemide and its biotransformation products by gas-liquid chromatography. A biexponential decay of serum furosemide concentrations vs. time was observed. Recovery of furosemide and its metabolites from urine in 24 hr varied between 30 and 98% of the administered dose. The excretion of unchanged drug accounted for 22.6-73.4% of the dose. The excretion of the glucuronide metabolite and 2-amino-4-chloro-5-sulfamoylanthranilic acid accounted for 3.3-40.4% and from 0.13-3.92% of the dose, respectively. Urinary excretion of furosemide was less in patients with, than in those without, myocardial infarction. Urinary excretion of the oxidative acidic metabolite was increased in patients with reduced creatinine clearance. The glucuronide metabolite of furosemide was the major biotransformation product in these patients with acute pulmonary edema.