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 met hod with ultraviolet absorbance detection has been developed to simult aneously 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 Nuc leosil 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 p hase, The detection was performed at 385 nm. The compounds were isolat ed from plasma by Bakerbond C-18 solid-phase extraction. The limit of quantitation was 10 ng/ml plasma for each compound investigated. The a ssay has been validated with respect to accuracy, precision and system suitability. All validated parameters were found to be within the nec essary limits, On the basis of the sensitivity, linearity and validati on parameters, the developed analytical method was found to be suitabl e 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 h uman 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 acety lator phenotypes the concentration of nerisopam was considerably highe r in plasma, while the level of its acetyl metabolite was higher in pl asma of fast acetylators.