A Sensitive Analytical Method for the Determination of a Novel Lipoxygenase Inhibitor, 4-Bromo-2,7-dimethoxy-3H-phenothiazin-3-one, in Plasma Using Reductive Electrochemical Detection

A reversed-phase high-performance liquid chromatographic assay using electrochemical detection in the reductive mode has been developed for the analysis of 4-bromo-2,7-dimethoxy-3H-phenothiazin-3-one (1) in plasma to determine drug absorption. Free drug in plasma in concentrations as little as 0.25ng/mL can be estimated with a mean coefficient of variation (CV) of 6.3 ± 2.6%. Metabolites which can be converted to the parent drug by acid hydrolysis can be quantified in concentrations of 10ng/mL or more, with a mean CV of 4.3 · 1.9%. To test the procedure, plasma was obtained from dogs receiving 14Clabeled 1. After acid hydrolysis of plasma, the electrochemical assay for parent drug showed good agreement with the radioactive equivalents in plasma, suggesting that parent drug and metabolites can be satisfactorily analyzed by this procedure.