Could local anesthesia while breast-feeding be harmful to infants?

Few studies have been carried out on the levels and possible toxicity of local anesthetics in breast milk after parenteral administration. The purpose of this study is to determine the amount of lidocaine and its metabolite monoethyl-glycinexylidide (MEGX) in breast milk after local anesthesia during dental procedures.

The study population consisted of seven nursing mothers (age, 23-39 years) who received 3.6 to 7.2 mL 2% lidocaine without adrenaline. Blood and milk concentrations of lidocaine and its metabolite MEGX were assayed using high-performance liquid chromatography. The milk-to-plasma ratio and the possible daily doses in infants for both lidocaine and MEGX were calculated.

The lidocaine concentration in maternal plasma 2 hours after injection was 347.6 +/- 221.8 microg/L, the lidocaine concentration in maternal milk ranged from 120.5 +/- 54.1 microg/L (3 hours after injection) to 58.3 +/- 22.8 microg/L (6 hours after injection), the MEGX concentration in maternal plasma 2 hours after injection was 58.9 +/- 30.3 microg/L, and the MEGX concentration in maternal milk ranged from 97.5 +/- 39.6 microg/L (3 hours after injection) to 52.7 +/- 23.8 microg/L (6 hours after injection). According to these data and considering an intake of 90 mL breast milk every 3 hours, the daily infant dosages of lidocaine and MEGX were 73.41 +/- 38.94 microg/L/day and 66.1 +/- 28.5 microg/L/day respectively.

This study suggests that even if a nursing mother undergoes dental treatment with local anesthesia using lidocaine without adrenaline, she can safely continue breastfeeding.