Determination of cisapride and norcisapride in human plasma using high-performance liquid chromatography with ultraviolet detection

A simple, rapid and reproducible high-performance liquid chromatographic assay for cisapride and norcisapride in human plasma is described. Samples of plasma (150 μl) were extracted using a C₁₈ solid-phase cartridge. Regenerated tubes were eluted with 1.0 ml of methanol, dried, redissolved in 150 μl of methanol and injected. Chromatography was performed at room temperature by pumping acetonitrile–methanol–0.015 M phosphate buffer pH 2.2–2.3 (680:194:126, v/v/v) at 0.8 ml/min through a C₁₈ reversed-phase column. Cisapride, norcisapride and internal standard were detected by absorbance at 276 nm and were eluted at 4.3, 5.3 and 8.1 min, respectively. Calibration plots in plasma were linear (r>0.998) from 10 to 150 ng/ml. Intraday precisions for cisapride and norcisapride were 3.3% and 5.4%, respectively. Interday precisions for cisapride and norcisapride were 9.6% and 9.0%, respectively. Drugs used which might be coadministered were tested for interference.