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

Background: Few studies have been carried out on the levels and possible to xicity of local anesthetics in breast milk after parenteral administration. The purpose of this study is to determine the amount of lidocaine and its metabolite monoethylglycinexylidide (MEGX) in breast milk after local anest hesia during dental procedures. Methods: The study population consisted of seven nursing mothers (age, 23-3 9 years) who received 3.6 to 7.2 mt 2% lidocaine without adrenaline. Blood and milk concentrations of lidocaine and its metabolite MEGX were assayed u sing high performance liquid chromatography. The milk-to-plasma ratio and t he possible daily doses in infants for both lidocaine and MEGX were calcula ted. Results: The lidocaine concentration in maternal plasma 2 hours after injec tion was 347.6 +/- 221.8 mug/L, the lidocaine concentration in maternal mil k ranged from 120.5 +/- 54.1 mug/L (3 hours after injection) to 58.3 +/- 22 .8 mug/L (6 hours after injection), the MEGX concentration in maternal plas ma 2 hours after injection was 58.9 +/- 30.3 mug/L, and the MEGX concentrat ion in maternal milk ranged from 97.5 +/- 39.6 mug/L (3 hours after injecti on) to 52.7 +/- 23.8 mug/L (6 hours after injection), According to these da ta 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 mug/L/day and 66. 1 +/- 28.5 mug/ L/day respectively. Conclusions: This study suggests that even if a nursing mother undergoes de ntal treatment with local anesthesia using lidocaine without adrenaline, sh e can safely continue breastfeeding.