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 t he internal standard for the assessment of lidocaine and vice versa. T he 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 prepar ed samples are chromatographed with a Merck LiChroCART(R) Superspher(R ) 60 RP-select B cartridge column, the local anesthetics are detected using UV-photometry and the concentration is calculated by comparing t he peak areas of the analyzed substance and the internal standard. Usi ng a sample volume of 1 ml plasma, concentrations of approximately 2.5 mu g/ml and 1 mu g/ml can be analyzed with a 95%-confidence interval of 2.5% or 5%, respectively. At higher or lower concentrations, accura te results can be obtained using smaller or larger plasma samples. The evolved analytical method allows the rapid and simple determination o f lidocaine and bupivacaine plasma levels at a wide range of concentra tions. It is suitable for research purposes as well as for routine ana lyses.