Measurable, but low, amounts of natalizumab are excreted into breastmilk in some women. The time of the peak level in breastmilk is often in the first week after the dose, but might be as long as 6 months with repeated doses. Limited information indicates that the drug is not measurable in the serum of breastfed infants. Most expert guidelines do not recommend avoiding breastfeeding with natalizumab.[1-4] Breastfeeding can resume immediately after injection; however, waiting for at least 2 weeks postpartum to resume therapy may minimize transfer to the infant.[5]