International Board of Certified Lactation Consultant (IBCLC) Practice Exam

What is the protein binding percentage threshold above which drugs do not easily transfer into breast milk?

1. Above 75%

2. Above 80%

3. Above 90%

4. Above 95%

The correct answer is: Above 90%

The protein binding percentage threshold above which drugs do not easily transfer into breast milk is generally considered to be above 90%. Drugs that are highly bound to plasma proteins are less likely to cross biological membranes, including the mammary gland, due to their larger size and the binding affinity to these proteins. When a drug is more than 90% bound to proteins, it typically remains in the bloodstream, reducing its availability to enter breast milk. Understanding the concepts of drug pharmacokinetics, including protein binding, is crucial for lactation consultants when counseling breastfeeding mothers about the safety of medications. A lower protein binding percentage indicates a higher likelihood that a drug will be available in free form to cross into the milk. Thus, careful consideration of this threshold can help ensure safe medication use during breastfeeding.