WHAT ARE DRUG TRANSPORTERS?

Transporters are membrane proteins whose primary function is to facilitate the flux of
molecules into and out of cells. Drug transporters did not evolve to transport specific drugs. Instead, their primary functions are to transport nutrients or endogenous
substrates, such as sugars, amino acids, nucleotides, and vitamins, or to protect the
body from dietary and environmental toxins. However, the specificity of these transporters
is not strictly restricted to their physiological substrates. Drugs that bear
significant structural similarity to the physiological substrates have the potential to be
recognized and transported by these transporters. As a consequence, these transporters
also play significant roles in determining the bioavailability, therapeutic efficacy, and
pharmacokinetics of a variety of drugs. Nevertheless, because drugs may compete
with the physiological substrates of these transporters, they are also likely to interfere
with the transport of endogenous substrates and consequently produce deleterious
effects on body homeostasis.