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 x 4.6 mm, 10 microm 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.