Rapid Ultraviolet Procedure for Measuring Doxepin and Some Doxepin Metabolites in Human Urine

A method is described for measuring doxepin-related material excreted in urine. Unchanged doxepin and certain doxepin metabolites are oxidized to doxepin ketone with KMnO4. The doxepin ketone is extracted with n -hexane and quantitated by ultraviolet spectrophotometry at the absorption maximum, 266 nm. This method is fast, reproducible, and measures a greater percentage of doxepin-related material than do existing gas—liquid chromatographic procedures. Doxepin ketone was measured to provide bio-availability data, for comparison of different formulations in humans.