Extradural administration of bupivacaine: pharmacokinetics and metabolism in pregnant and non-pregnant women.

We found a similar time (about 0.4 h) to maximum serum concentration after extradural administration of bupivacaine 1.78 (SD 0.27) mg kg-1 to six pregnant patients at term, 1.58 (0.13) mg kg-1 to six women younger than 65 yr and 1.50 mg kg-1 to six women older than 65 yr. There were no significant differences in terminal half-life. No unconjugated 4'-hydroxy-bupivacaine was detected in the serum and urine of pregnant patients, in contrast with the other groups. The pregnant patients had significantly greater serum concentrations of the N-dealkylated metabolite, N-desbutyl-bupivacaine (DBB), than the non-pregnant groups. In contrast with 4'-hydroxy-bupivacaine, no conjugated forms of bupivacaine and desbutyl-bupivacaine were detected in urine. The mean total urinary excretion of bupivacaine and its metabolites and their conjugates varied between 2.46 and 3.22% of the total dose administered in the three patient groups, indicating that both 4'-hydroxylation and N-dealkylation are minor metabolic pathways in man.