Pregnant women are often complicated with diseases including viral or
bacterial infections,
epilepsy,
hypertension, or pregnancy-induced conditions such as depression and
gestational diabetes that require treatment with medication. In addition,
substance abuse during pregnancy remains a major public health problem. Many drugs used by pregnant women are off label without the necessary dose, efficacy, and safety data required for rational dosing regimens of these drugs. Thus, a major concern arising from the widespread use of drugs by pregnant women is the transfer of drugs across the placental barrier, leading to potential toxicity to the developing fetus. Knowledge regarding the
ATP-binding cassette (ABC) efflux transporters, which play an important role in
drug transfer across the placental barrier, is absolutely critical for optimizing the therapeutic strategy to treat the mother while protecting the fetus during pregnancy. Such transporters include
P-glycoprotein (P-gp, gene symbol ABCB1), the
breast cancer resistance
protein (BCRP, gene symbol ABCG2), and the
multidrug resistance proteins (MRPs, gene symbol ABCCs). In this review, we summarize the current knowledge with respect to developmental expression and regulation, membrane localization, functional significance, and genetic polymorphisms of these
ABC transporters in the placenta and their relevance to fetal
drug exposure and toxicity.