A Comparison of the Blood Levels and Urinary Excretion of Ethionamide and Prothionamide in Man

The blood levels and urinary excretion of the anti-mycobacterial drugs ethionamide and prothionamide have been compared after oral dosage in man. High pressure liquid chromatographic methods were used to determine the two closely related thioamides and their microbiologically active sulphoxide metabolites after the ingestion of both single and combined doses of the two drugs. Both drugs were rapidly eliminated from the body, the half-life for the urinary excretion and removal from the plasma of prothionamide being slightly less than that of ethionamide. Less than 0.1% of the orally administered doses were excreted unchanged in the faeces. Plasma concentrations of ethionamide and its sulphoxide metabolite were substantially higher than those of prothionamide and prothionamide sulphoxide. The implications of these findings for the use of ethionamide or prothionamide in the treatment of lepromatous leprosy are discussed.