Placental transfer of lidocaine hydrochloride after prolonged continuous maternal intravenous administration

We treated a patient with arrhythmia during pregnancy with prolonged intravenous administration of lidocaine hydrochloride. This was a case of twin-to-twin transfusion syndrome and the arrhythmia was caused by ritodrine therapy. In total, 14.1 g lidocaine (50 mg.hr-1 for 282 hr) were used. Since there are no descriptions of human placental transfer of lidocaine after such a prolonged continuous intravenous administration, we measured lidocaine concentrations in maternal and fetal serum, and in the amniotic fluid (AF) at delivery. Fetal serum lidocaine concentrations (donor: 0.83 microgram.ml-1; recipient: 0.82 microgram.ml-1) were lower than in the maternal serum (1.6 micrograms.ml-1), while the AF lidocaine concentrations (donor: 1.05 micrograms.ml-1; recipient: 1.04 micrograms.ml-1) were higher than those of the fetal sera. The fetal/maternal concentration ratios of lidocaine were 0.52 for the donor and 0.51 for the recipient, which were similar to those described previously after administration of lidocaine in labour.