Plasma levels of real and "apparent" hydralazine in man and rat.

Derivatization of hydralazine in plasma under acidic conditions yields values for the concentrations of "apparent" hydralazine that are dependent on the pH in the derivatization step. The results have been explained by postulating the existence of acid-hydrolyzable conjugates of unknown structure. These metabolites appear to be present in rat and human plasma after oral dosing. Procedures have been developed for the selective analysis of hydralazine or its acid-labile conjugates, and applied to measurements of plasma concentrations in rat and man.