In recent years, significant advancements have been made in our knowledge of breastfeeding and the medicinal treatment of nursing mothers with MS, particularly for monoclonal antibodies. We know there is little transfer of monoclonal antibodies to breast milk due to their high molecular weight (around 145 000 daltons), and most of it is denatured in the infant's gastrointestinal tract. Furthermore, there is little or no absorption of antibodies through the infant's mucosa (12). As a general rule, we believe there is sufficient evidence to recommend that breastfeeding is safe in women receiving monoclonal antibody therapy. Paradoxically, the evidence on use in nursing mothers is better for rituximab – which is used to treat multiple sclerosis off label – than for the medications with marketing authorisation. The older medications glatiramer acetate and interferons are also safe, but are far less potent.
As a general rule, we believe there is sufficient evidence to recommend that breastfeeding is safe in women receiving monoclonal antibody therapy
Colostrum, which is produced in the first few days after childbirth, has a different composition from mature breast milk (9). As the data for breastfeeding mostly relate to more than 14 days after childbirth, we recommend that most nursing mothers wait until after this period to start MS treatment. Premature infants can have higher absorption and poorer excretion of medication than other infants, which may indicate that some should wait more than 14 days.
The duration of treatment effect varies considerably between different MS drugs. Cladribine, alemtuzumab and, to some extent, rituximab and ocrelizumab have a long-lasting pharmacodynamic effect. For these medications, it is relatively easy to adapt breastfeeding to the treatment regime.
Natalizumab and sphingosine-1-phosphate receptor modulators have a more short-lived effect and are associated with symptom flare-ups after treatment is discontinued. Women who discontinued these medications before or during pregnancy are particularly at risk of severe relapses during the postpartum period (13). We therefore recommend that women treated with a sphingosine-1-phosphate receptor modulator before pregnancy change to a monoclonal antibody if they want to breastfeed.