Which statement best describes placental transfer?

Which statement best describes placental transfer?

• A. Ionized, hydrophilic drugs cross easily.
• B. Very high molecular weight ensures crossing.
• C. Strong binding to plasma proteins
• D. Non-ionized, lipophilic drugs cross more readily.

Answer: (D)

Placental transfer mainly occurs by passive diffusion across the placental membranes. The barrier is lipid-rich, so drugs that are non-ionized and lipophilic readily dissolve in the membrane and diffuse down their concentration gradient into fetal blood. Smaller molecules cross more easily than large ones, and only the unbound (free) drug can diffuse, so high protein binding reduces transfer. In contrast, ionized or hydrophilic drugs cross poorly. Therefore, non-ionized, lipophilic drugs cross more readily, making that statement the best description of placental transfer.

Placental transfer mainly occurs by passive diffusion across the placental membranes. The barrier is lipid-rich, so drugs that are non-ionized and lipophilic readily dissolve in the membrane and diffuse down their concentration gradient into fetal blood. Smaller molecules cross more easily than large ones, and only the unbound (free) drug can diffuse, so high protein binding reduces transfer. In contrast, ionized or hydrophilic drugs cross poorly. Therefore, non-ionized, lipophilic drugs cross more readily, making that statement the best description of placental transfer.