Abatacept is a large fusion protein that interferes with T-cell activation. It has a molecular weight of 92,000, so only small amounts are expected to enter breastmilk and absorbed by the infant.[1] One case report indicates that amounts in milk are very low and do not appear to affect the breastfed infant. Waiting for at least 2 weeks postpartum to resume therapy may minimize transfer to the infant.[2] Some professional guidelines consider abatacept to be acceptable during breastfeeding.[3,4] However, until more information is available an alternate drug may be preferred, especially while nursing a newborn or preterm infant.