Liquid chromatographic method for the determination of lidocaine and monoethylglycine xylidide in human serum containing various concentrations of bilirubin for the assessment of liver function.

A high-performance liquid chromatographic method is described for determination of lidocaine (2-(dietyloamino)-N-(2,6-dimetylofenylo) acetamid) and its metabolite, monoethylglycine xylidide (MEGX), in human serum containing various concentration of bilirubin. Lidocaine and its metabolite were extracted from human serum using dichloromethane. After separation of the layers and freezing at -32 degrees C, the organic layer was decanted and evaporated under a stream of nitrogen. The sample was dissolved in the mobile phase (12% acetonitrile in 15mM potassium dihydrogen orthophosphate, pH 3.0), and after separation on a Supelcosil LC-8-DB column, the analytes were measured by ultraviolet detection at 205nm. Trimethoprim (TMP) was used as the internal standard. The recovery of the examined analytes ranged from 95.7 to 97.9% for lidocaine and from 98.0 to 99.9% for MEGX. The lower limit of quantification (LLOQ) was established at 200microg/l for lidocaine and at 10microg/l for MEGX. The choice of suitable conditions for chromatographic separation of lidocaine and its metabolite MEGX allowed the elimination of the influence of endogenous bilirubin on the result of analysis.