International Board of Certified Lactation Consultant (IBCLC) Practice Exam

What aspect of a drug greatly affects its ability to pass into breast milk?

1. The patient's age

2. The drug's protein binding

3. The frequency of dosage

4. The method of administration

The correct answer is: The drug's protein binding

The ability of a drug to pass into breast milk is significantly influenced by the drug's protein binding characteristics. Drugs that have a high affinity for binding to plasma proteins are less likely to transfer into breast milk because only the unbound or free portion of the drug is available to cross biological membranes, including the membranes of breast epithelial cells. When a drug is highly protein-bound, it remains predominantly in the mother's bloodstream and has limited availability to enter the milk compartment. Conversely, drugs that are loosely bound or unbound to proteins have a higher likelihood of passing into breast milk. This property is crucial for lactation consultants and healthcare providers when considering medication use in breastfeeding mothers, as it helps to assess the potential exposure of the infant to various medications through breast milk. Other factors, while they may play a role in pharmacokinetics and drug levels, do not directly determine the extent to which a drug permeates into breast milk in the same manner as protein binding does.