Simultaneous determination of bupivacaine and its two metabolites, desbutyl- and 4'-hydroxybupivacaine, in human serum and urine.

A sensitive and selective high-performance liquid chromatographic (HPLC) method for the determination of bupivacaine and its two metabolites, desbutyl- and 4'-hydroxybupivacaine, in human serum and urine is described. Bupivacaine, both metabolites and the internal standard, etidocaine, are extracted with diethyl ether and then back-extracted into an acidic aqueous phase. After subsequent extraction into diethyl ether, evaporation and reconstitution in the mobile phase, bupivacaine and the metabolites are determined by HPLC using a reversed-phase C8 column with tetrahydrofuran-potassium phosphate buffer (8:92, v/v, pH 2.4) as the mobile phase. The sensitivity of the method is 10 micrograms/l for bupivacaine and both metabolites and the extraction efficiencies are 95, 54 and 92% for bupivacaine and desbutyl- and 4'-hydroxybupivacaine, respectively. The reproducibility of the method is good, the coefficients of variation varying between 1.8 and 7.4% in the concentration range 0.10-2.00 mg/l. The procedure was applied to human serum and urine samples from two elderly women who had been operated on under epidural analgesia (plain bupivacaine, 1.5 mg/kg) because of uterine prolapse.