International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Which drug characteristic can decrease the amount of a drug that enters breast milk?

1. High molecular weight

2. Low lipid solubility

3. High protein binding

4. All of the above

The correct answer is: All of the above

The correct answer encompasses several characteristics that can influence the transfer of drugs into breast milk. Each of the listed drug characteristics plays a role in decreasing the amount of the drug that enters breast milk. High molecular weight leads to reduced permeability across biological membranes, including the mammary gland. Drugs that are larger molecules are less likely to be excreted into breast milk compared to smaller molecules, limiting their availability for transfer. Low lipid solubility indicates that a drug is less likely to diffuse across cell membranes, as many drugs that easily enter breast milk are lipid-soluble. Therefore, drugs with low lipid solubility tend to remain in the bloodstream rather than entering breast milk, decreasing the amount that can be transferred. High protein binding refers to the degree to which a drug binds to plasma proteins. Drugs that are highly bound to proteins in the blood are less likely to be free in the circulation, reducing their likelihood of being secreted into breast milk. When a drug is primarily protein-bound, only the unbound fraction can enter breast milk, which results in lower concentrations in the milk. Considering these factors collectively illustrates how the drug characteristics work together to limit the presence of the drug in breast milk. This understanding is essential for lactation consultants when advising breastfeeding individuals