Easy and fast LC–MS/MS determination of lidocaine and MEGX in plasma for therapeutic drug monitoring in neonates with seizures

A fast liquid chromatography–tandem mass spectrometry with electrospray ionization method was developed and validated for simultaneous quantification of lidocaine and its active metabolite MEGX in 10 μL of plasma of neonates with seizures. The sample preparation consists of an easy protein precipitation sample pre-treatment with methanol. Chromatographic separation was achieved on a Alltima HP C18-EPS 150 mm × 2.1 mm column with an isocratic mobile phase of 0.1% (v/v) ammonium acetate in purified water–0.1% (v/v) formic acid in acetonitrile (70:30, v/v). The analytes were detected with a Thermo Scientific triple quadrupole Quantum Access with positive ionization. Ions monitored in the selected reaction monitoring (SRM) mode were m/z 235.2 → 86.6 for lidocaine (at 3.35 min), m/z 207.1 → 58.8 for MEGX (at 2.75 min) and 280.1 → 86.7 for 3-nitrolidocaine (internal standard, at 3.20 min). The method was validated over a linear range of 0.2–18.0 mg/L for lidocaine and MEGX, using 3-nitrolidocaine as the internal standard. The lower limit of quantification (LLQ) was 0.2 mg/L for lidocaine and MEGX. The within-run and between-run CV (%) were lower than 6.9% for both lidocaine and MEGX. Recoveries were in the range of 99.4% to103.6%. Observed LC–MS/MS matrix effects were −6.2% for MEGX (ion suppression) and were negligible for lidocaine and the internal standard (i.e. <0.1%). Compared to other bioanalytical articles published in medical literature (PubMed) during the last 15 years that described LC–MS/MS methods for quantification of lidocaine in human plasma, our method uses less plasma, has a shorter and more simple sample pre-treatment and has a short run time.