Key result
Epidural bupivacaine administration in laboring women resulted in lower umbilical venous plasma concentrations than maternal venous concentrations, due to greater protein binding in maternal plasma.
Observational (n=31)
Differences in maternal and fetal plasma concentrations of bupivacaine are driven by greater protein binding in maternal plasma rather than differences in unbound drug.
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Supports maternal protein binding limiting fetal bupivacaine exposure; leaves open prospective validation for obstetric dosing.
The maternal venous and umbilical venous plasma concentrations of bupivacaine were determined at delivery following epidural administration of the drug to 31 women in labor. In each case the umbilical venous plasma concentration of bupivacaine was lower than the maternal venous plasma concentration. There was no significant difference between the concentration of unbound bupivacaine in umbilical venous and maternal venous plasma at delivery. The difference in umbilical and maternal plasma concentrations of bupivacaine appears to be a consequence of greater bupivacaine binding to maternal than to fetal total plasma protein. The intersubject variation of the ratio of bupivacaine concentration in fetal plasma/bupivacaine concentration in maternal plasma was found to be related to individual variation in the extent of protein binding of bupivacaine in maternal and umbilical plasma and correlated positively with the variation of the ratio of total protein concentration in umbilical and maternal plasma.
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Thomas et al. (1976) conducted an observational in Women in labor (n=31). Epidural bupivacaine was evaluated on Maternal venous and umbilical venous plasma concentrations of bupivacaine. Epidural bupivacaine administration in laboring women resulted in lower umbilical venous plasma concentrations than maternal venous concentrations, due to greater protein binding in maternal plasma.
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