Identification of a biliary metabolite of cisapride

Radiolabeled cisapride was administered orally to male Wistar rats. The drug was metabolized extensively, resulting in the formation of a large number of urinary and faecal metabolites. In bile-cannulated rats a major metabolite was excreted with the bile whose structure could not be elucidated with the aid of the registered electron impact and desorption chemical ionization spectra. Therefore the biliary metabolite was subjected to extensive analytical procedures combining fast atom bombardment mass spectrometry, thermospray liquid chromatography/mass spectrometry, nuclear magnetic resonance and ultraviolet analysis. The results of this study allowed the identification of the biliary metabolite as the O-sulphate of metabolically formed 3′-hydroxycisapride.