I am not familiar with myasthenia or the medicine you mentioned. The best suggestion I can make would be to ask questions to the medical professionals you'll work with. Ask your OB, as the nurses at the hospital when you deliver, call the hospital now and ask for a lactation consultant - ask them. If you select a pediatrician before your baby is born, ask them... Ask the pharmacist where you get your meds filled... The literature that would come with your meds should have information about what to do if you're breastfeeding while taking the meds. Best of luck!