Identification of the urinary metabolites of 14C-bumetanide in the rat and their excretion by rats and dogs.

Unchanged bumetanide, 3-(n-butylamino)-4-phenoxy-5-sulfamoylbenzoic acid, and five metabolites were excreted in the urine of rats given 50 mg of 14C-labeled drug per kg intravenously. The metabolites, which were identified by mass spectrometry and/or nuclear magnetic resonance spectroscopy, arose by metabolic alteration of the n-butyl sidechain. In metabolites I-V, the butylamino group was converted to -NHCH2CH2CH2COOH, -NHCH2CH2CH2CH2OH,, -NHCH2CH2CHOHCH3, -NHCH2CH2CHOHCH2OH and -NH2, respectively. The total urinary and fecal excretion of labeled drug and metabolites after iv and oral administration of 14C-bumetanide was estimated in dogs given 0.5 mg/kg and in rats given 5 mg/kg. In the dog, the primary excretion product was unchanged drug, although evidence was obtained that the acyl glucuronide of bumetanide was secreted in dog bile. The major metabolite excreted by the rat was I, and negligible quantities of intact drug were excreted in the urine after oral or iv administration. Optical activity was found for the two metabolites that contained a chiral center (III and IV), indicating that they were formed by a stereoselective hydroxylation.