Medications and breastfeeding

Drugs may transfer into milk if they reach high concentrations in maternal plasma, are low in molecular weight (<800 Da), are low in protein binding and pass easily into the brain. Other factors, such as the oral bioavailability of the medication to the baby, are also very important. Many medications, for instance, can be destroyed in the baby’s gut or are stored in the mother’s liver, and may never reach the mother’s plasma.

Drugs can enter milk by passive diffusion from the maternal plasma compartment and the maternal milk compartment. Medications normally pass from maternal plasma into the lactocytes, but they must pass through both bilayer lipid membranes of the lactocytes to reach the milk. During the first three days post-partum, however, tight junctions between lactocytes can be open and permit enhanced drug transfer into the milk.

Medications that inhibit milk production

Drug-related inhibition of milk production may occur via inhibition of prolactin from the pituitary, inhibition of oxytocin release and via direct effects on lactocytes. A comprehensive list of drugs and medications that may inhibit milk production can be found at http://toxnet.nlm.nih.gov/newtoxnet/lactmed.htm

General guidelines for most medications and drugs during breastfeeding

• Avoid using medications unless necessary, including herbal drugs
• Most medications are suitable if the relative baby dose is less than 10 per cent, however, consultation with a medical professional is advised
• Safe medications while breastfeeding generally should have short half-lives, high protein binding, low oral bioavailability in the baby and high molecular weight
• Medical professionals should refer to an up-to-date database of drug interactions which can occur during lactation before prescribing a new drug to breastfeeding mums.