The peak is when you do not want the mother to breastfeed her infant, rather, wait until the peak is subsiding or has at least dropped significantly. Remember, drugs enter breastmilk as a function of the maternal plasma concentration. The higher the mom's plasma level, the greater the entry of drug into her milk. If possible, choose drugs that have short peak intervals, and don't let mom breastfeed when it peaks. This lists the percentage of maternal protein binding.
Most drugs circulate in the blood bound to plasma albumin.
If a drug is highly protein bound, it cannot exit the plasma compartment as well. The higher the percentage of binding, the less likely the drug is to enter the maternal milk. So try to choose drugs that have high protein binding, in order to reduce the infants exposure to the medication. The oral bioavailability refers to the ability of a drug to reach the systemic circulation after oral administration. It is generally a good indication of the amount of medication that is absorbed into the blood stream of the patient.