Ofatumumab-exposed breastfeeding in multiple sclerosis patients

Background: In Europe, ofatumumab is approved for breastfeeding, but data on its transfer into breast milk and clinical experience are lacking. Objective: To analyze (1) health, development, and adverse events after live vaccination of ofatumumab-exposed breastfed infants and (2) detectability of ofatumumab in breast milk, and to calculate the relative infant dose (RID) using two methods, the traditional method and a second method considering maternal exposure to multiple ofatumumab doses and extended collection period. Methods: In this observational study, clinical data were collected by standardized telephone interviews up to 2 years postpartum. Breastmilk samples were analyzed by enzyme-linked immunosorbent assay. Results: Twelve mothers started ofatumumab-exposed breastfeeding between 0.6 and 19.6 months postpartum. Infants showed neither abnormalities in infections, antibiotic use, or hospitalizations nor developmental delay. Five infants with available B cells had normal levels. Eight (66.7%) infants received live vaccines during/after exposed breastfeeding. None had complications. Ofatumumab concentration in breast milk varied widely between a median RID of average concentration 0.027% (range: 0.019%–0.115%) using method 1 and 2.912% (range: 1.301%–12.322%) using method 2. Conclusion: Ofatumumab-exposed breastfeeding did not adversely affect infants’ health or development. Despite higher RIDs using the more appropriate method 2, the risk of substantial antibody absorption by infants appears to be low.