The Absorption, Excretion, and Metabolic Fate of Ethambutol in Man1

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Abstract
The absorption, excretion and concentrations in the plasma of ethambutol-C14 following oral administration of 25 mg/kg of body weight was investigated. The absorption of the drug which is rapid though not quantitative, results in peak values of 5 [gamma]/ml of plasma approximately 4 hours after administration. From 79-94% of an oral dose and 82% of an intravenous injection of the drug are recovered in the urine and feces for 144 hours after administration. There are no indications of drug accumulation. The metabolism of ethambutol is not extensive, and from 8-15% of a given oral or intravenous dose appears in the urine as metabolites in 24 hours. Metabolite-II was identified as the aldehyde intermediate in the oxidation of ethambutol and metabolite-I, as the final oxidation product of the drug, 2,2[image]-(ethylenediimino)-di-l-butyric acid. Daily doses of the drug over a 6-month period have no effect on its metabolism.