Simultaneous assay of thioridazine and its major metabolites in plasma at single dosage levels with a novel report of two ring sulfoxides of thioridazine.

A highly sensitive and selective method of analysis of plasma for thioridazine and its major metabolites, including two isomers of the ring sulfoxide, is presented. It is suitable for following the metabolism of thioridazine for 24 hr after a single dose. The method involves extraction of the materials from plasma, high-performance liquid chromatographic separation, and postcolumn oxidation and fluorometric detection. The sensitivity of the method to thioridazine and its metabolites is 2 ng/ml. Recoveries ranged from 87.8 to 100.6% at levels between 20 and 400 ng/ml.