Simple Method for Quantification of Lidocaine and Its Metabolite Monoethylglycine Xylidide in Plasma

We developed a simple and fast LC method quantifying lidocaine and its metabolite monoethylglycinexylidide (MEGX) in plasma. An extraction of liquid-liquid with dichloromethane and sodium hydroxide, was done using 500 μL of plasma or serum, with a UV detection at 210 nm. The results showed linearity of r = 0.996 for lidocaine and 0.998 for MEGX. Precision and accuracy showed coefficient of variation within an acceptable range. Stability test was acceptable for a period of 90 days. Levels were assayed for two patients, in the first, 1,256.14 ng mL⁻¹ of lidocaine and 17.79 ng mL⁻¹ of MEGX were obtained while in the second the levels for the substances were 1,194.33 and 10.47 ng mL⁻¹. This simple and fast method is reliable and can be recommended for the quantification of lidocaine and MEGX in plasma.