Objective: This study compares the human placental transport of glyburide, glipizide, chlorpropamide, and tolbutamide.
Study design: The recirculating single cotyledon human placenta model tested maternal-to-fetal transport in term placentas perfused immediately after delivery. Drug levels were measured by high-performance liquid chromatography and liquid scintillation spectrometry, and transport rates were calculated by comparing maternal and fetal concentrations.
Results: The transport of these substances differed significantly over a tenfold range (analysis of variance, p < 0.0008). A significant association exists by multiple linear regression between drug transfer and molecular weight, dissociation constant, and the octanol-water partition coefficient (R2 = 0.91, p < 0.0001).
Conclusions: There is significant variability in human placental transfer rates of the oral hypoglycemics, which strongly correlates with molecular properties. These data suggest that less fetal exposure may occur with second-generation sulfonylureas and anticipate that regression models may be useful in selecting agents that minimize placental transport to the fetus.