IBCLC Practice Exam 2026 – Complete Preparation Guide

When selecting medications for breastfeeding mothers, the property of high molecular weight is particularly significant because it influences how much of a drug passes into breast milk and ultimately reaches the infant. Drugs with a high molecular weight tend to have larger molecules that are less likely to diffuse through cell membranes, making them less likely to enter the breast milk in significant quantities. This characteristic helps to minimize potential exposure to the breastfeeding infant, which is a primary concern when prescribing medications to lactating mothers.

In contrast, other properties such as long half-lives and high lipid solubility may increase the likelihood of significant drug levels in maternal plasma and subsequently in breast milk, potentially exposing the infant to higher amounts of the medication. High oral bioavailability indicates that a drug is readily absorbed when taken orally, which may also raise concerns for the amount that could be present in breast milk. Therefore, high molecular weight is prioritized to ensure safer options for lactating mothers and their babies.