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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(
Distribution from Mother to Fetus & Placental barrier
‒ The maternal and foetal blood vessels are separated by the placental barrier.
‒ Drugs cross the placental membrane by passive transcellular diffusion.
‒ The placental membrane has very tight junctions, so lipophilic solutes are
transported and distributed faster than hydrophilic solutes.
‒ The large surface area of fetal villi, however, allows even hydrophilic drugs to
cross into the fetal circulation to some extent.
‒ The fetal blood has fewer plasma proteins, so more of the drug is present as free
fraction in the fetal circulation.
‒ Additionally, the other membrane barriers in the fetus are not as well developed
as those in the mother, and drug may distribute into fetal tissues (such as the brain)
more readily.
‒ Thus, the placental barrier is not as effective as the blood-brain barrier.
‒ So, care must be taken while administration of all types of drugs during
pregnancy because of the uncertainty of their harmful effects on developing fetus.
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