Breastfed infants exposed to lamotrigine faced a low risk of toxic effects

Aim We aimed to investigate plasma lamotrigine concentrations and clinical effects in infants exposed to lamotrigine through breastfeeding. Methods This was a retrospective study of mother–infant dyads in a clinical follow‐up programme in Stockholm, Sweden. Data were collected from medical records. Results We included 47 breastfed infants, born from 2011 to 2021, with a median gestational age of 39 + 6 weeks/days and a median birth weight of 3420 g. The median lamotrigine concentration in the infants' plasma was 2.5 (range 2.5–14.0) μmol/L. These concentrations correlated significantly with both the maternal plasma concentrations and the maternal doses ( R = 0.79, p < 0.001 versus R = 0.54, p < 0.001). During the follow up, lamotrigine concentrations within the reference range for epilepsy treatment were detected in six (14%) infants and one had clinical symptoms that were probably related to lamotrigine exposure. Liver transaminases were elevated in three of 21 infants. All infants whose mothers had a dose of 150 mg or less had undetectable plasma concentrations and no symptoms during follow up. Conclusion Infants exposed to lamotrigine through breastfeeding had a low risk of toxic effects. All infants whose mothers had low lamotrigine doses had unmeasurable plasma concentrations and no symptoms of lamotrigine exposure. These low‐risk infants might be offered a simplified follow up.