Answer:
the similarity of the drug molecule to other molecules that are transported into the target cells
Step-by-step explanation:
Selective transport of the substance occurs when the plasma membrane allows only selective substances to pass through it while inhibiting the transport of other molecules. Charge, polarity, size of the substances to be transported and the presence /absence of carriers and channels in the plasma membrane are some of the factors that determine which substance would cross the plasma membrane.
If a drug is required to enter the cytoplasm of the target cell, it should be similar to the other substances that can enter the cell. The drug should have nearly identical charge, polarity, structure, size, etc. as that of the permitted substances to enter the cell. For example, a drug similar to glucose can enter the cells that have Glut transporters in their plasma membrane.