Adrenergic Antagonists: Chemistry and Classification of β-Receptor Blockers

β-receptor blockers or β-adrenoceptor antagonists bind to β receptors and inhibit catecholamine-mediated sympathetic responses.

All β blockers are competitive antagonists but differ in characteristics such as adrenoceptor subtype affinity, lipophilicity, and α-blockade ability.

β blockers are categorized as either nonselective or selective.

The first β blocker was dichloroisoprenaline with partial agonist activity. Further research led to the development of propranolol, which was a pure antagonist but nonselective agent.

Next, propranolol analogs were further explored to obtain clinically effective drugs with β₁-selectivity. For instance, practolol and atenolol are  β₁-selective.

Few selective β₁ antagonists, like metoprolol, showed cardioselective actions.

Additionally, β blockers are also categorized generation-wise. The first generation includes older, nonselective molecules, while the second comprises cardioselective molecules.

The third generation includes newer drugs such as labetalol and carvedilol with additional α blocking or vasodilatory action. These drugs are therapeutically important in treating heart ailments and hemodynamic disorders.