Simultaneous Determination of Paroxetine, Risperidone and 9-Hydroxyrisperidone in Human Plasma by High-Performance Liquid Chromatography with Coulometric Detection

A method for the simultaneous determination of paroxetine, risperidone and its main metabolite 9-hydroxyrisperidone in human plasma has been developed. The procedure involved a multistep solid-phase liquid extraction with an internal standard. The drugs were separated on a cyano column followed by coulometric detection. This method described here has sufficient sensitivity to quantitate paroxetine accurately in the range 5–500 ng/ml with a lower limit of detection of 1 ng/ml and risperidone and its main metabolite 9-hydroxyrisperidone in the range 2–100 ng/ml with a lower limit of detection of 1 ng/ml when 1 ml of plasma was used for the analysis. The precision, accuracy and specificity have been proven, and show that the method is reliable for clinical studies and routine drug monitoring.