Selective and sensitive determination of amisulpride in human plasma by liquid chromatography–tandem mass spectrometry with positive electrospray ionisation and multiple reaction monitoring

The development of a validated liquid chromatography–tandem mass spectrometry (LC-MS/MS) method with positive electrospray ionisation (ESI(+)) and multiple reaction monitoring (MRM) for the selective and sensitive bioanalytical determination of amisulpride, a substituted benzamide derivative, in human plasma is described. Plasma was cleaned up using a liquid–liquid extraction (diisopropylether:dichloromethane = 1:1 (v/v)) procedure. The chemically related drug sulpiride was used as internal standard (ISTD) and a primary calibration function was established in the concentration range of 0.50–500.52 ng/ml for amisulpride in plasma by triple analysis of the corresponding calibration standards. A linear relationship between concentration and signal intensity (given as peak area ratio analyte/ISTD) was obtained (linear regression: r = 0.9999). A lower limit of quantification (LLQ) of 0.50 ng/ml was used during measurement of study plasma samples. Satisfying results of within-day precision (CV = 0.79 to 1.98%) and accuracy (mean relative deviation: −1.68 to 3.58%) and between-day precision (CV = 1.34 to 4.62%) and accuracy (mean relative deviation: −1.73 to −3.77%) as well as of recovery (amisulpride: 81.74 to 84.83%; sulpiride: 58.65%) and selectivity investigations confirmed the high reliability of this established LC-MS/MS method. Sufficient stability of amisulpride in plasma was achieved during freeze–thaw-cycles, for storage periods of 24 h at room temperature and 20 days at <−20 °C as well as in extracts (storage conditions: <−20 °C, 6 days and 7 °C, 6 days) with mean relative deviations between − 2.83 and 2.91%. An example of a pharmacokinetic profile determined after administration of an amisulpride 200 mg dose in a pilot study is given in this paper. A peak plasma concentration (Cmax) of 522.58 ng/ml was achieved after 3.55 h (tmax). Corresponding values of areas under the plasma concentration–time curve (AUC) of 3405.35 ng h/ml (AUC0−∞) and 3306.54 ng h/ml (AUC0−tlast) were obtained. The terminal plasma elimination half-life (t1/2) was 10.36 h.