High-performance liquid chromatographic determination of bupivacaine in plasma samples for biopharmaceutical studies and application to seven other local anaesthetics.

A sensitive analytical procedure for bupivacaine dosing in plasma samples by reversed-phase high-performance liquid chromatography is described. After a two-step extraction, the analysis was performed using a C18 column and a mobile phase of 0.01 M sodium dihydrogen-phosphate (pH 2.1)-acetonitrile (80:20, v/v). The extraction yield of bupivacaine from plasma was 73.5 +/- 5.1% (mean +/- S.D., n = 10). The within-day and between-day reproducibilities at a concentration of 100 ng/ml were 2.1% and 5.6%, respectively (n = 10). Calibration curves were linear (r2 = 0.9996) between 5 and 1000 ng/ml. The limit of detection, defined by a signal-to-noise ratio of 3:1, was 2 ng/ml. The accuracy at a concentration of 100 ng/ml was 2.3%. This method could be applied to the plasma analysis of seven other local anaesthetics (articaine, etidocaine, lidocaine, mepivacaine, pramocaine, procaine and tetracaine). The procedure was used in bioavailability studies of bupivacaine-loaded poly(D,L-lactide) (i.e. PLA) and poly(D,L-lactide-co-glycolide) (i.e. PLGA) microspheres after subcutaneous and intrathecal administrations in rabbits.