Mechanisms of drug transfer across the human placenta.

In this review we summarized literature data on the mechanisms of human placental drug transport studied in the isolated perfused placental cotyledon, placental membrane vesicles or trophoblastic cell cultures. Overall human placental drug transport rarely exceeds the transfer of flow-dependent and membrane-limited marker compounds. Interestingly, relatively often placental drug transfer appeared to be much smaller, indicating impaired trans-placental transport, depending on the physico-chemical characteristics of the drug or placental factors such as tissue binding or metabolism. Although in perfusion studies overall human placental drug transport occurs by simple diffusion, at the membrane level several drug transport systems have been found, mainly for drugs structurally related to endogenous compounds.