International Board of Certified Lactation Consultant (IBCLC) Practice Exam

What molecular weight is considered too high for a medication to easily transfer into breast milk?

1. 500 Daltons

2. 700 Daltons

3. 800 Daltons

4. 900 Daltons

The correct answer is: 800 Daltons

The molecular weight of a medication is a critical factor in determining its ability to transfer into breast milk. Typically, substances with a molecular weight of less than 500 Daltons are more likely to pass into breast milk relatively easily. As the molecular weight increases, particularly over 800 Daltons, the likelihood of extensive transfer into breast milk decreases significantly. Choosing 800 Daltons as the threshold is based on the general understanding that medications or compounds with a molecular weight above this range tend to have reduced permeability through biological membranes, including the barriers necessary for them to enter breast milk. This is due to larger molecules facing more difficulty diffusing through lipid membranes, thus limiting their availability in breast milk. Therefore, when considering the transfer of medications into breast milk, recognizing that 800 Daltons is a point at which the transfer becomes notably restricted is important for healthcare providers and lactation consultants in assessing the safety and potential effects of medications on breastfeeding infants.