From what was written, it sounds to me as if the mother is getting one
treatment a week.  Is that right?

If this is so, though methotrexate and its active metabolites have a
long half life, it might be possible for this mother to have her
treatment, perhaps go off breastfeeding for 2 or 3 days, and then resume
until the next feeding.  Indeed, if she has a good milk supply, she
could pump extra during the breastfeeding days and give it to the baby
when she cannot.

She could also have the amount of methotrexate in her milk measured and
when it is close to zero, she could start breastfeeding.

Complicated, but it might work.

Jack Newman, MD, FRCPC