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Metabolism and excretion of bupivacaine in man: a comparison with mepivacaine.

SUMMARY The biotransformation and urinary excretion of the local analgesic drug bupivacaine and its homologue mepivacaine have been studied in five healthy male volunteers in whom the urine was maintained at pH 5. Each drug (43.4 mg) was given intravenously to four subjects. Blood samples were taken for 8 hours and urine was collected for 24 hours: both were analyzed by gas-chromatography. A mean of 16 per cent of the mepivacaine given was excreted unchanged, and only 6 per cent of the dose of bupivacaine. The production of the N-dealkylated metabolite of both drugs, pipecolylxylidine (PPX) was confirmed in all subjects. More PPX was excreted after bupivacaine (5.11 per cent of the dose) than after mepivacaine (1.23 per cent). Since, when PPX itself was given to two subjects, almost half was excreted unchanged in the urine, this metabolite could not account for a large proportion of either drug. Only a small percentage of the dose of the drugs was recovered by the method used, and more might be accounted for by undetected water-soluble metabolites. Blood concentrations of bupivacaine fell more rapidly than those of mepivacaine in the first 2 hours, and thereafter they declined at similar rates.