Specific and sensitive analysis of nefopam and its main metabolite desmethyl-nefopam in human plasma by liquid chromatography–ion trap tandem mass spectrometry

Abstract: A specific and sensitive liquid chromatography–tandem mass spectrometric (LC–MS–MS) method using an ion trap spectrometer was developed for quantitation of nefopam and desmethyl-nefopam in human plasma. Nefopam, desmethyl-nefopam and the internal standard (ethyl loflazepate) were extracted in a single step with diethyl ether from 1mL of alkalinized plasma. The mobile phase consisted of acetonitrile with 0.1% formic acid (50:50, v:v). It was delivered at a flow-rate of 0.3mL/min. The effluent was monitored by MS–MS in positive-ion mode. Ionisation was performed using an electrospray ion source operating at 200°C. Nefopam and desmethyl-nefopam were identified and quantified in full scan MS–MS mode using a homemade MS–MS library. Calibration curves were linear over the concentration range of 0.78–100ng/mL with determination coefficients >0.996. This method was fast (total run time<6min), accurate (bias<12.5%), and reproducible (intra- and inter-assay precision<17.5%) with a quantitation limit of 0.78ng/mL. The high specificity and sensitivity achieved by this method allowed the determination of nefopam and desmethyl-nefopam plasma levels in patients following either intermittent or continuous intravenous administration of nefopam. [Copyright &y& Elsevier]