The metabolism of (-)-ephedrine in man

The metabolic fate of orally administered (-)-[14C]-ephedrine has been studied in 3 human subjects and the urinary excretion of metabolites determined quantitatively by solvent extraction, paper chromatography and reverse isotope dilution procedures. Following an oral dose of the drug (0.35 mg/kg, 1.6 muCi), 97% of the dose was excreted in the urine within 48 h, 88% in the first 24 h. Unchanged drug was the major urinary excretory product (53-74%), with N-demethylation occurring to a variable extent (8-20%) although there was little interindividual variation in urine pH. Oxidative deamination was also variable (4-13%); the main identified products of this were benzoic acid (free and conjugated) and 1,2-dihydroxy-1-phenylpropane (free and conjugated). No phenolic metabolites could be detected, and thus it would appear that these compounds cannot be implicated in the acquisition of tolerance to ephedrine which can occur on repeated dosage.