STUDIES ON THE METABOLISM OF ISONIAZID .2. INFLUENCE OF PARA-AMINOSALICYLIC ACID ON THE METABOLISM OF ISONIAZID BY MAN

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Abstract
The influence of para-aminosalicylic acid (PAS) on the metabolism of isoniazid by man has been investigated. In one study, the urinary excretion of isoniazid and its total metabolites (total isonicotinic acid derivatives) has been determined following administration of isoniazid alone and in combination with PAS. No marked effect of the adjunctive drug was noted. In a second study, the plasma concentrations of isoniazid and total hydrazides and the urinary excretion of these materials were measured simultaneously. Although urinary excretion of unchanged isoniazid was found to be very slightly increased in some of the subjects studied, effects on plasma concentrations of this compound were essentially nonexistent. These findings provide no support for the concept that therapeutic doses of PAS block acetylation or otherwise alter the metabolism of isoniazid in man.