Development of a HPLC-system for quantitative measurement of lidocaine and bupivacaine in patients plasma during postoperative epidural pain therapy.

A HPLC method was developed for the simultaneous quantitative analysis of lidocaine and bupivacaine in plasma, with bupivacaine serving as the internal standard for the assessment of lidocaine and vice versa. The samples are prepared by diethyl ether-extraction of the alkalified plasma and re-extraction using diluted sulphuric acid. This allows the elimination of interfering medication and plasma proteins. The prepared samples are chromatographed with a Merck LiChroCART Superspher 60 RP-select B cartridge column, the local anesthetics are detected using UV-photometry and the concentration is calculated by comparing the peak areas of the analyzed substance and the internal standard. Using a sample volume of 1 ml plasma, concentrations of approximately 2.5 micrograms/ml and 1 microgram/ml can be analyzed with a 95%-confidence interval of 2.5% or 5%, respectively. At higher or lower concentrations, accurate results can be obtained using smaller or larger plasma samples. The evolved analytical method allows the rapid and simple determination of lidocaine and bupivacaine plasma levels at a wide range of concentrations. It is suitable for research purposes as well as for routine analyses.