A rapid and simple microassay for lidocaine in human blood plasma using gas-liquid chromatography with nitrogen...

Lidocaine is widely used in antiarrhythmic therapy, and the need to monitor the drug concentration in the blood of patients receiving lidocaine is well established. We have developed a new assay for lidocaine designed for the routine clinical therapeutic drug monitoring laboratory. A 100-microliter aliquot of blood plasma is treated with 50 microliters of internal standard solution and the mixture alkalinized. The drug and internal standard are extracted with toluene and analyzed by nitrogen-detection gas-liquid chromatography. A single extraction is used, and no solvent evaporation is required, resulting in a simple and rapid procedure. Using the single-point standard, the within-day coefficient of variation (CV) was 6.4%, while the between-day CV was 7.4%. Monoethylglycinexylidide, the major plasma metabolite of lidocaine, and several drugs potentially present in patients receiving lidocaine were shown not to interfere. The procedure has significant advantages over previously published similar methods.