DETERMINATION OF DAPOXETINE, AN INVESTIGATIONAL AGENT WITH THE POTENTIAL FOR TREATING DEPRESSION, AND ITS MONO-DESMETHYL AND DI-DESMETHYL METABOLITES IN HUMAN PLASMA USING COLUMN-SWITCHING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A column-switching high-performance liquid chromatographic (HPLC) method is described for the determination of dapoxetine and its mono- and di-desmethyl metabolites in human plasma. The analytes, including an internal standard, were extracted from plasma at basic pH with hexane-ethyl acetate. The organic extract was evaporated to dryness and the residue reconstituted with acetonitrile. The analytes were separated from late-eluting endogenous substances on a Zorbax RX-C-8 pre-column. The front-cut fraction containing the analytes was further separated on a second RX-C-8 column. The analytes were detected by their native fluorescence, using excitation and emission wavelengths of 230 and 330 nm, respectively. The limit of quantitation was determined to be 20 ng/ml, and the response was linear from 20 to 200 ng/ml. The method has been successfully applied to human plasma samples in a Phase I study.