How do potency, efficacy and selectivity differ?

Why

Use concentration-response curves with sufficient dose range, stable controls and an explicit response scale. EC50 or IC50 is a context-dependent potency parameter and does not always equal binding affinity. Emax captures response amplitude in a particular assay.

A partial agonist can have high apparent potency yet a lower maximal effect than a full agonist. Selectivity requires appropriate comparator targets and assays measured under comparable conditions. A compound may be selective among purified kinases but not among phenotypes in cells.

For example, compound A halves an enzyme signal at 20 nM but suppresses several unrelated enzymes at similar exposures, while compound B requires 200 nM yet has far fewer measurable off-target effects. Compound B may be preferable depending on intended exposure and safety. Always identify whether the readout measures target binding, pathway signaling or growth.