New method for the chiral evaluation of mirtazapine in human plasma by liquid chromatography

A simple, rapid and sensitive high-performance liquid chromatography (HPLC) method was developed for the enantioselective analysis of the new antidepressant drug mirtazapine in human plasma. The procedure involved liquid–liquid extraction using toluene, followed by liquid chromatography coupled to UV detection at 292 nm. The chromatographic separation of the (+)-(S)- and (−)-(R)-enantiomers of mirtazapine was achieved on a Chiralpak AD column (250 mm × 4.6 mm, 10 μm particle size) protected with a CN guard column, using hexane–ethanol (98:2, v/v) plus 0.1% diethylamine as the isocratic mobile phase, at a flow rate of 1.2 ml/min. The total analysis time was less than 12 min per sample. The recoveries of (+)-(S)- and (−)-(R)-mirtazapine were in the 88–111% range with a linear response over the 6.25–625 ng/ml concentration range for both enantiomers. The quantification limit (LOQ) was 5 ng/ml. Within-day and between-day assay precision and accuracy were studied at three concentration levels (10, 50 and 250 ng/ml). For both mirtazapine enantiomers, the coefficients of variation (CV) and deviation from the theoretical value were lower than 15% at all concentration levels. The method proved to be suitable for pharmacokinetic studies.