Determination of dibucaine and its metabolites in human urine by high-performance liquid chromatography with fluorescence detector

A high-performance liquid chromatographic (HPLC) method using a fluorescence detector is described for the simultaneous determination of dibucaine and its metabolites (M-4, M-8 and M-10) in human urine. Urine samples from obstetric patients were chromatographed in a reversed-phase system. When a ultraviolet detector (320 nm) was used, some interfering peaks appeared on the chromatogram, but this interference could be overcome by employing a fluorescence detector (Ex 330 nm and Em 440 nm) instead. The calibration curves were linear in the range of 0.05-5.0 μg/ml for all compounds and the detection limits of dibucaine and its metabolites were about 5 ng/ml in urine. The urinary excretion of dibucaine and its metabolites by obstetric patients infused with Percamine S® in the spinal cord were determined. The mean cumulative amounts of dibucaine, M-4, M-8 and M-10 excreted during 10 h after administration were 1.1, 10.5, 3.5 and 1.1 % of the dose, respectively. The total urinary excretion was 16.2% of the dose. This method is sufficiently sensitive and specific to permit the determination of dibucaine and its metabolites in biological fluids.