efflux transporter

Some cells act like tireless bouncers, throwing drug molecules back out the moment they try to enter. An efflux transporter is a membrane protein that uses energy to pump drugs out of cells against their concentration gradient, actively limiting how much drug accumulates inside the cell or behind a barrier.

Most are ATP-binding cassette (ABC) transporters, including P-glycoprotein, the multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP). They sit in strategic places — the gut lining (reducing oral absorption), the blood–brain barrier (keeping drugs out of the brain), the kidney and liver (promoting excretion) and the placenta (protecting the fetus). Their job is essentially to expel a broad range of foreign molecules.

Efflux transporters have wide therapeutic significance. They limit the brain penetration and oral bioavailability of many drugs, drive multidrug resistance in cancer cells and microbes, and are sources of drug interactions when one drug inhibits or induces the pump and changes another drug's distribution or excretion.