Pharmacokinetics of drug transfer into breastmilk

Very few drugs are licensed for use by breastfeeding mothers. This does not, in itself, imply risk. There are expert sources which provide information on studies and pharmacokinetics which allow clinicians to make an assessment of the amount of drug passing through milk to the baby and any potential risks. The passage of drugs into breastmilk is governed by several factors: the oral bioavailability of a drug and the half-life of the drug. Research has shown that more drugs are prescribed for breastfeeding mothers in the immediate postpartum period than at any other time. The bioavailability is defined as the fraction of the dose which reaches the systemic circulation intact. The lower the oral bioavailability, the safer the drug is for a breastfeeding mother to take. The extent to which a drug is bound to plasma proteins in the maternal bloodstream influences the amount that is available to pass into milk.