To the Editor The study by Birnbaum et al¹ investigated infants’ antiepileptic drug (AED) exposure if mothers receiving AEDs were breastfeeding by comparing the percentage differences of mothers’ AED blood concentrations with their respective infants’ AED blood concentrations. For lamotrigine, infant-to-mother percentages had high variability between newborns, with concentrations ranging between 0.6% and 90.3%. Given that lamotrigine is likely a lipid-soluble medication,² we wonder if infants with higher body fat composition (ie, infants who were large for gestational age), compared with the infants who were normal or small for gestational age, had a higher concentration of lamotrigine. If the blood concentration of lamotrigine in infants who were large for gestational age was significantly higher, the safety of breastfeeding in those infants should be evaluated more cautiously.