Breastmilk and infant serum levels of amiodarone and its active metabolite are somewhat unpredictable, but can be high during breastfeeding. The infant receives an estimated dose of amiodarone plus desethylamiodarone ranging from 3.5 to 45% of the mother's weight-adjusted amiodarone dose, with a median dose of about 11%.[1-4] Infant serum levels of the drug plus metabolite range from 14 to 74% of simultaneous maternal levels, with the higher values reflecting transplacental passage of the drug.[2-4] In addition to possible cardiac effects, these compounds contain a large amount of iodine which may be released during metabolism. Thyroid dysfunction was reported in one breastfed infant. Even if the drug were discontinued at birth, the mother would continue to excrete amiodarone and its metabolite (and possibly large amounts of iodine) into breastmilk for days to weeks.
Some investigators believe that breastfeeding can be undertaken during maternal amiodarone use with periodic monitoring of infant cardiac and thyroid function status,[5,6] especially if only a single dose of amiodarone is given.[7,8] Infant serum levels of amiodarone and desethylamiodarone may be useful for ruling out cardiac effects of the drug. If hypothyroidism develops, therapy should be promptly initiated.