Permeability of human chorion laeve to diazepam and meperidine.

In vitro placental permeability to diazepam (Valium) and meperidine (Demerol) in excess of that measured for antipyrine, suggest that these compounds will diffuse across placental tissue in vivo at a maximal or perfusion-limited rate. Such findings correspond to the high fetal blood levels reported for these substances following maternal administration and indicate that these lipid-soluble analgesics cross this tissue by transcellular as well as extracellular pathways.