Transporter

The term transporter typically refers to a kind of endogenous, membrane-bound, protein-based structure that physically moves drugs and endogenous small and macromolecules across cell membranes into and out of cells ¹. Hundreds of such transporters exist and the exact mechanism of action behind each one is dependent upon which transporter, in particular, is being discussed. Nevertheless, drugs can elicit a wide variety of effects on transporters including manipulating the release of certain chemicals through transporters or the direct use of such structures for transit towards targets in and out of cells. 

Each transporter in DrugBank is considered a [bio entity] and is associated with a unique identification code that starts with "BE". For example, the code for Solute carrier family 22 member 2 is BE0003647. 

Note that targets, enzymes, carriers, and transporters may switch roles depending on the drug to which they bind based on each drug's unique pharmacodynamic and pharmacokinetic profiles.