Drug transporters

Membrane transporters are present in a variety of anatomical locations and organ systems throughout the body. Transporters control the absorption, distribution, intracellular penetration, and excretion of numerous drugs. ATP-binding cassette (ABC) and solute carrier (SLC) superfamilies comprise the majority of clinically relevant transport proteins. In intestinal and liver epithelia, transport proteins control the access of certain medications to systemic circulation. In the kidney, transporters may facilitate or impair drug excretion depending on their specific location and function. However, it is at the blood-brain barrier (BBB) where membrane transporters regulate access of endogenous and exogenous compounds to the central nervous system (CNS). This chapter will review the common drug transport proteins in the intestine and liver as they impact the systemic exposure of drugs that exert their primary pharmacologic effects in the CNS; drug transporters in the kidney that may influence the excretion of such agents will also be addressed. The primary focus of this chapter will be drug transport of centrally acting agents at the BBB, primarily via the efflux transporter and ABCB1 gene product, P-glycoprotein (P-gp). Additional transport proteins will be considered for their documented or putative involvement in drug interactions involving centrally acting medications. Lastly, approaches to circumvent the influence of drug efflux at the BBB will be considered, including modulation of centrally located membrane transporters. Approaches to developing drugs that bypass the effects of efflux transporters at the BBB will also be discussed.