Determination of fluvoxamine and paroxetine in human serum with highperformance liquid chromatography and ultraviolet detection

We optimized an isocratic reversed phase high performance liquid chromatography with ultraviolet detection to quantify, simultaneously, the selective serotonin reuptake inhibitors (SSRIs) fluvoxamine and paroxetine in human serum. Fluvoxamine was used as the internal standard for the determination of paroxetine, and paroxetine served as internal standard for the fluvoxamine assay. The method involved a pre-column technique for the on-line liquid-solid extraction with direct injection of serum samples and for their pre-concentration. Automation was achieved by column switching. The chromatographic separation was performed on an Ultrasep ES 100 CN-column with acetonitrile/methanol/phosphate buffer (58/19/23, v/v/v) as mobile phase. A linear relationship (r(2) > 0.99) was noted between the concentrations of fluvoxamine or paror;etine and the detector signal. The lower limits of detection in human serum of fluvoxamine and paroxetine were 5 and 2 mu g/L, respectively. The accuracy of the quality control samples deviated by +/-8% with a within-day and between-day precision of less than 12.1%, and 10.5% for fluvoxamine and paroxetine, respectively. The method is presently being applied in our clinic for the routine therapeutic drug monitoring of both SSRIs.