Determination of risperidone in plasma by high-performance liquid chromatography with electrochemical detection: application to therapeutic drug monitoring in schizophrenic patients.

A highly sensitive high-performance liquid chromatography method with electrochemical detection for the determination of risperidone in plasma has been developed. Remoxipride is used as an internal standard. A simple one-step extraction with 25% methylene dichloride in pentane is used to isolate the drug from the plasma. This is followed by high-performance liquid chromatography analysis on a cyano column with electrochemical detection. Under the experimental conditions described here, commonly coadministered drugs and other antipsychotic drugs did not interfere with the analysis of either risperidone or the internal standard. Also, the available two metabolites of risperidone did not interfere in the assay. This method has sufficient sensitivity to quantitate risperidone accurately at 0.1 ng/mL, when 1 mL of plasma was used for the analysis, with a coefficient of variation of < 9%. This method has been successfully used in the determination of plasma levels of risperidone in schizophrenic patients treated with 4-, 6-, and 8-mg oral doses per day.