No information is available on the clinical use of alemtuzumab during breastfeeding. Because alemtuzumab is a large protein molecule with a molecular weight of 145,454 Da, the amount in milk is likely to be very low.[1] It is also likely to be partially destroyed in the infant's gastrointestinal tract and absorption by the infant is probably minimal.[2] Until more data become available, alemtuzumab should be used with caution or avoided in nursing mothers during treatment for multiple sclerosis, especially while nursing a newborn or preterm infant.[3-7] Waiting for at least 2 weeks postpartum to resume therapy may minimize transfer to the infant.[7] The manufacturer recommends that women not breastfeed during treatment and for at least 3 months following the last dose.