Simultaneous analysis of a new cardiotonic agent, MDL 17,043, and its major sulfoxide metabolite in plasma by high-performance liquid chromatography.

MDL 17,043 or 1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl]-2H-imidazol-2-one, is a new cardiotonic agent being developed for the treatment of congestive heart failure. This communication describes a sensitive and selective analytical procedure for the simultaneous analysis of MDL 17,043 and its major oxidative metabolite in plasma. The method involves addition of internal standard and organic solvent extraction, followed by separation with high-performance liquid chromatography and detection by ultraviolet absorption. The assay has good precision and accuracy. Evidence for the positive identification of the sulfoxide metabolite is also presented.