Simultaneous determination of fluoxetine, citalopram, paroxetine, venlafaxine in plasma by high performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-MS/ESI).

Abstract Fluoxetine, citalopram, paroxetine and venlafaxine have been widely used in the treatment of depression. However, no study has been conducted to determine the four drugs simultaneously by high performance liquid chromatography–electrospray ionization mass spectrometry (HPLC–MS/ESI). Objective: To establish a new, rapid and sensitive HPLC–MS/ESI method for simultaneous determination and screening in human plasma of the four most commonly prescribed nontricyclic antidepressants: fluoxetine, citalopram, paroxetine and venlafaxine. Methods: The analytes in plasma were extracted by solid-phase-extraction column after samples had been alkalinized. The HPLC separation of the analytes was performed on a MACHEREY-NAGEL C 18 (250 mm × 4.6 mm, 5 μm, Germany) column, using water (formic acid 0.6‰, ammonium acetate: 30 mmol/l)–acetonitrile (35:65, v/v) as mobile phase, with a flow-rate of 0.85 ml/min. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and were detected in the selected ion recording (SIR) mode. Results: The calibration curves were linear in the 5.0–1000.0 ng/ml range for all compounds, all of them with coefficients of determination above 0.9900. The average extraction recoveries for all the four analytes were above 73.2%. The methodology recoveries were higher than 95.0%. The limits of detection (LODs) were 0.5, 0.3, 0.3 and 0.1 ng/ml for fluoxetine, citalopram, paroxetine and venlafaxine, respectively. The intra- and inter-day variation coefficients were less than 15.0%. Conclusion: The method is accurate, sensitive and simple for routine therapeutic drug monitoring (TDM) as well as toxicologic screening, and for the study of the pharmacokinetics and metabolism of the four drugs.