Comment from Anonymous

I am submitting Tamaki et al. 2024, “Breast milk concentrations of acetaminophen and diclofenac: unexpectedly high mammary transfer of the general-purpose drug acetaminophen,” in support of the requested acetaminophen warning. This study is relevant because it shows that acetaminophen exposure should not be viewed as limited to pregnancy. In postpartum women, acetaminophen transferred readily into breast milk, with breast milk exposure comparable to maternal plasma exposure and a reported milk-to-plasma ratio of 1.048. This is especially important because modern opioid-sparing postpartum pain protocols often include scheduled, around-the-clock acetaminophen while mothers are breastfeeding. FDA should expand its review and any required warning language to address the full perinatal exposure window, including pregnancy, labor and delivery, postpartum maternal dosing, breastfeeding, NICU use, and direct infant dosing. At minimum, mothers should be informed that acetaminophen readily transfers into breast milk and that repeated scheduled use during breastfeeding may expose the infant during a developmentally vulnerable period.