Women with bipolar disorder are vulnerable to postpartum illness, and it is generally recommended that mothers continue treatment with a mood stabilizer throughout the postpartum period to reduce their risk of relapse; however, this recommendation is complicated by the all mood stabilizers are secreted into the breast milk, although their concentrations appear to vary considerably (Chaudron and Jefferson, 2000).

Lamotrigine (Lamictal) is being used with increasing frequency in childbearing women.  We last reported on its use in of lamotrigine in breastfeeding women in 2005. At that time, several small studies indicated that lamotrigine was passed to infants through the breast milk in relatively high doses.  Infant serum levels ranged from 23 to 50% of levels found in the mothers’ serum.

The largest study comes from Dr. Jeffrey Newport and colleagues and includes a total of 30 women taking lamotrigine and their nursing infants.  The authors reported that milk/plasma ratios were highly variable, ranging from 5.7% to 147.1%.  The mean milk/plasma ratio was 41.3%.  This type of variability has been reported in studies of antidepressants and other medications in nursing infants, indicating that milk/plasma ratios may of limited utility in estimating the extent of exposure in the nursing infant.

Using measurement of maternal and infant plasma concentrations, it was estimated that the relative infant dose (RID) of lamotrigine was 9.2% and that the theoretical infant dose (TID) was o.51 mg/kg per day.  This RID of 9.2% is lower than the RID cutoff of 10% frequently used as an empiric cutoff for assuming safety during lactation.  The authors caution that clinicians should be advised that this rule of thumb is arbitrary and has not been objectively verified.  It is reassuring, however, that this dose is considerably lower than doses of lamotrigine used to treat seizures in infants.

Maternal reports and review of pediatric records revealed no adverse events in the nursing infants.

More research is required to better assess the safety of lamotrigine in nursing infants; however, these findings are reassuring and are consistent with previous reports.  Lamotrigine levels were detected in all infants assessed; however, no adverse events were reported. While the majority of professional and nutritional organizations support breast milk as the ideal form of nutrition for the infant in the first year of life, women taking psychotropic medications, such as lamotrigine, must weigh the benefits of breastfeeding against the risks of exposure to medication.

Ruta Nonacs, MD, PhD

Chaudron LH, Jefferson JW. Mood stabilizers during breastfeeding: a review. J Clin Psychiatry. 2000 Feb;61(2):79-90.

Newport DJ, Pennell PB, Calamaras MR, et al.  Lamotrigine in Breast Milk and Nursing Infants: Determination of Exposure. Pedistrics. 2008. 122(1):e223-e231.