Hi, I am delurking to ask a question. I am working with a mom who was taking 300mg of mexiletine 3x a day while pregnant. It is for heart arrhythmia. The baby is 3 weeks old and she is breastfeeding and still taking the mexiletine. Her pediatrician wants her to continue breastfeeding, but wants information on the mexiletine. LLL's Breastfeeding Answer Book says no effect on baby or lactation; the USPDI says don't breastfeed; Clinical Pharmacy (Aug 1991) says concentration in milk are low and cannot be detected in the plasma of breastfed infants. I have faxed these three pieces of info to the pediatrician. The sources conflict, so if I'm confused, I'm sure the mother is and maybe the pediatrician too. Does anyone have anything else? Also, does anyone have a study on long-term effects on a BF baby who's mother is taking mexiletine - if there are any long-term effects? Thank you. Deb Wirtel, LLLL St. Louis [log in to unmask]