Determination of risperidone and its major metabolite 9-hydroxyrisperidonein human plasma by reversed-phase liquid chromatography with ultraviolet detection

A simple and sensitive high-performance Liquid chromatographic (HPLC) metho d with UV absorbance detection is described for the quantitation of risperi done and its major metabolite 9-hydroxyrisperidone in human plasma, using c lozapine as internal standard. After sample alkalinization with 1 ml of NaO H (2 M) the test compounds were extracted from plasma using diisopropyl eth er-isoamylalcohol (99:1, v/v). The organic phase was back-extracted with 15 0 mu l potassium phosphate (0.1 M, pH 2.2) and 60 mu l of the acid solution was injected into a C-18 BDS Hypersil analytical column (3 mu m, 100x4.6 m m I.D.). The mobile phase consisted of phosphate buffer (0.05 M, pH 3.7 wit h 25% H3PO4)-acetonitrile (70:30, v/v), and was delivered at a flow-rate of 1.0 ml/min. The peaks were detected using a UV detector set at 278 nm and the total time for a chromatographic separation was about 4 min. The method was validated for the concentration range 5-100 ng/ml. Mean recoveries wer e 98.0% for risperidone and 83.5% for 9-hydroxyrisperidone. Intra- and inte r-day relative standard deviations were less than 11% for both compounds, w hile accuracy, expressed as percent error, ranged from 1.6 to 25%. The limi t of quantitation was 2 ng/ml for both analytes. The method shows good spec ificity with respect to commonly prescribed psychotropic drugs, and it has successfully been applied for pharmacokinetic studies and therapeutic drug monitoring. (C) 2000 Elsevier Science B.V. All rights reserved.