Definition of Efflux and Influx Transporters

Drug transporters can be categorized as efflux or influx transporters according to the
direction in which they transport substrate across the cell membranes. This classification
is often observed in the literature where drug transport studies are performed
at the cellular level. With this definition, transporters that pump the substrates out of
the cells are called efflux transporters, whereas transporters that transfer substrates
into cells are called influx transporters.