A Liquid Chromatographic Method for the Simultaneous Determination of Promethazine and Three of Its Metabolites in Plasma Using Electrochemical and UV Detectors

A new assay method has been developed for the quantitation of promethazine (PMZ) with a sensitivity and reproducibility as good as any previously reported method. This method is also capable of quantitatively determining three metabolites of PMZ (monodemethylated, sulphoxidated, and monodemethylated sulphoxidated PMZ), which has not been previously described. The method uses high-performance liquid chromatography with amperometric and UV detection simultaneously and requires only one extraction step from serum with chloroform. The method uses trifluoperazine as the internal standard. The limit of detection level for PMZ is 1.0 ng/mL when a 0.2-mL specimen of plasma is assayed. A validation study is also conducted for evaluating the recovery, precision, linearity of response, sensitivity, and selectivity of the method.