On the fate of furosemide in man

Summary

³⁵S-furosemide was administered orally (n=7) or i.v. (n=2) to healthy subjects. The average gastrointestinal uptake estimated by comparison of the urinary recovery of label and the areas under the plasma curves after the two routes of administration was 65%. The half life of radioactivity in the plasma after oral³⁵S-furosemide was 90 ± 17 min (estimated on the slope between 2 and 6 h); the corresponding figure after³⁵S-furosemide i.v. was 47–53 min (slope 0.5–4 h). There was probably a slower phase after 4–6 h. Fractionation of labelled material in urine from two subjects demonstrated that approximately two thirds of the label recovered at 24 h had the same chromatographic properties as furosemide. A major part of the metabolite(s) was probably furosemide glucuronide. There was no evidence that 4-chloro-5-sulfamoylanthranilic acid was formed in man. The total urinary recovery of label (5–7 d) after oral and intravenous administration was 55.1±3.2 (mean±SD) and 82–84%, respectively. After³⁵S-furosemide i.v., 6–9% of the label was recovered in faeces, and it could not be accounted for solely by biliary excretion of furosemide.