Purpose: We investigated the effect of pregnancy on the kinetics of lamotrigine (LTG), passage of LTG over the placenta and the excretion of the drug in breast milk.
Methods: We used high-performance liquid chromatography to determine concentrations of LTG in plasma and in breast milk in a woman who was treated with LTG monotherapy during pregnancy and lactation.
Results: Plasma levels of LTG decreased as pregnancy progressed. The ratio of dose to plasma concentration was 5.8 times higher at delivery and 3.6 times higher in late pregnancy as compared with 5 months postpartum, suggesting enhanced clearance of LTG during pregnancy. The concentration ratio of umbilical cord to mother's plasma was 1.2 indicating extensive passage of LTG over the placenta. The LTG plasma concentration in the newborn was still 48 h after birth similar to the plasma levels of the mother at delivery and in the umbilical cord. The ratio of milk to plasma concentration was 0.6 2 weeks after delivery and the plasma concentration in the breast-fed child was 25% of the mother's plasma levels. No adverse effects were observed in the newborn.
Conclusions: The kinetics of LTG may be influenced by pregnancy to such a degree that dose adjustments may be indicated. Due to an extensive passage of LTG into breast milk, and a slow elimination in the newborn, LTG concentrations in the nursed infant may reach levels at which pharmacological effects can be expected.