High-performance liquid chromatographic determination of bupivacaine in human serum

A selective high-performance liquid chromatographic method for the determination of bupivacaine in human serum is described. The technique is based on a single extraction of the drug from alkalinized serum with a mixture of hexane-isopropanol-chloroform. Desmethyldoxepin is used as internal standard. The chromatographic system consists of a home-packed Nucleosil C8 (10 microns) column; the mobile phase is acetonitrile--0.05 M potassium phosphate buffer (pH 3.3) (28:72, v/v). The method can accurately measure serum bupivacaine concentrations down to 20 micrograms/l using 500 microliters of sample. The coefficient of variation for intra-assay variability of bupivacaine is 2.1% (n = 13) and for inter-assay variability of bupivacaine 5.7% (n = 11) at 1.00 mg/l. The calibration graph is linear over the range 0.02-5.00 mg/l and the extraction efficiency is 91.8 +/- 3.8% (+/- S.D., n = 7). The method is accurate and sensitive for both clinical and pharmacokinetic studies on bupivacaine in man. The method is applied to the analysis of serum samples obtained from orthopaedic patients during both spinal and epidural analgesia.