In drug treatment, selectivity is very important in order to have the desired drug effect and to avoid possible adverse effects. This example shows the affinity of 3 different beta-adrenergic antagonists for the β1 and β2 receptor, respectively.
It can be deduced from the graphs, that propranolol is not selective: it has the same affinity for both β1 and β2. Metoprolol, however, is selective for β1: it has a high affinity for β1 and a low affinity for β2. Butoxamine is selective for β2 and not for β1.