Simultaneous determination of nerisopam, a novel anxiolytic agent showing polymorphic metabolism, and its N-acetyl metabolite from human plasma by a validated high performance liquid chromatographic method.

A sensitive reversed-phase high-performance liquid chromatographic method with ultraviolet absorbance detection has been developed to simultaneously determine the concentrations of nerisopam (EGIS-6775) and its N-acetyl metabolite (EGIS-7649) from human plasma. The separation of the investigated compounds and internal standard was achieved on a Nucleosil 7 C(18) column with 2 mM heptanesulphonic acid containing 0.04 M phosphoric acid-acetonitrile-methanol (70:25:5, v/v), pH 2.7 mobile phase. The detection was performed at 385 nm. The compounds were isolated from plasma by Bakerbond C(18) solid-phase extraction. The limit of quantitation was 10 ng/ml plasma for each compound investigated. The assay has been validated with respect to accuracy, precision and system suitability. All validated parameters were found to be within the necessary limits. On the basis of the sensitivity, linearity and validation parameters, the developed analytical method was found to be suitable for the determination of nerisopam and its N-acetyl metabolite from human plasma and for application in pharmacokinetic studies and human drug monitoring. The pharmacokinetic parameters obtained from twelve human volunteers are reported. It was found that nerisopam acetylation is polymorphic: the volunteers with fast or slow acetylator phenotypes produced significantly different plasma concentrations. In slow acetylator phenotypes the concentration of nerisopam was considerably higher in plasma, while the level of its acetyl metabolite was higher in plasma of fast acetylators.