No information is available on the clinical use of caplacizumab during breastfeeding. Because caplacizumab is a large protein molecule with a molecular weight of about 28,000 Da, the amount in milk is likely to be very low and absorption is unlikely because it is probably destroyed in the infant's gastrointestinal tract. Use of the drug after 2 weeks postpartum may minimize transfer to the infant.[1] Until more data become available, caplacizumab should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant. Some opinion recommends that patients with acquired thrombotic thrombocytopenic purpura not breastfeed because anti-platelet sIgA might be present in milk and may adversely affect the infant.[2]