It is clear that women with bipolar disorder are at high risk for relapse during the immediate postpartum period (Viguera 2000). There is evidence that the resumption of lithium prior to or within 24-48 hours of delivery can significantly reduce the risk of postpartum illness (Cohen 1995). While this intervention is the current standard of care for this high risk population, women have historically been instructed to avoid breastfeeding while taking lithium based on early reports suggesting high levels of lithium in the breast milk and several cases of lithium toxicity in nursing infants (Schou 1973). While the American Academy of Pediatrics guidelines are less restrictive in their current recommendation, they do urge caution. However, systematic studies regarding the levels of exposure to lithium in nursing infants and the potential risks of this exposure have been lacking.
In a recent study from Dr. Adele Viguera at the Center for Women’s Mental Health presented at the annual meeting of the American Psychiatric Association, 10 women taking lithium and their nursing infants were evaluated. Lithium levels in milk, as well as infant and maternal serum levels of lithium, were measured at approximately 6 weeks postpartum. Infant thyroid and renal function were also assessed. In this group of women, lithium carbonate dose averaged 841 mg/day (range 600-1200 mg/day). The average lithium concentration in breast milk was 0.36 ± 0.11 mmol/L (range <0.1 – 0.51) or 51% (range 17%-73%) of the maternal serum levels (average of 0.72 ± 0.22 mmol/L, range 0.41 – 1.16). Corresponding infant serum levels averaged 0.15 ± 0.07 mmol/L (range 0.09-0.30). Eight of the 10 infants had levels below 0.2 mmol/L. There were no adverse events reported in 9 of the10 infants; one infant had slightly elevated TSH (thyroid stimulating hormone) that soon normalized once lithium was discontinued.
Although the sample size in this study was relatively small, it is thus far the largest systematic study quantifying exposure to lithium in children nursed by mothers taking lithium. While early reports raised concerns regarding exposure to high levels of lithium in nursing infants, this study suggests that lithium levels in infants are relatively low and were about 25% of maternal levels. Furthermore, the incidence of serious adverse events in babies exposed to lithium through breast milk was low.
Given the many benefits of breastfeeding, some women taking lithium may opt to nurse their infants. While we have little data regarding the long-term effects of exposure to lithium contained within the breast milk, it appears that the risk of serious adverse events in the nursing infant is relatively low. Nonetheless, infants are vulnerable to the same side effects as adults, including changes in thyroid and renal functioning; thus, close clinical monitoring of infants exposed to lithium through breast milk is recommended. This monitoring should include measurement of lithium levels, TSH, BUN and creatinine every 6-8 weeks while the child is nursing.
Ruta Nonacs, MD PhD
Viguera AC, Nonacs R, Cohen LS, Tondo L, Murray A, Baldessarini RJ. 2000. Risk of recurrence of bipolar disorder in pregnant and nonpregnant women after discontinuing lithium maintenance. Am J Psychiatry 157:179-184.