Irreversible antagonist

Irreversible antagonist is a type of pharmacological antagonist that forms a covalent bond with their target receptor, resulting in permanent inactivation. This is in contrast to reversible antagonists, which bind non-covalently and can be displaced.

Mechanism of Action

Irreversible antagonists exert their effects by permanently binding to the active site of the receptor. This is usually achieved through the formation of a covalent bond, which is a strong type of chemical bond that cannot be broken under normal physiological conditions. As a result, the receptor is permanently inactivated and cannot be activated by its natural ligand.

Examples

One of the most well-known examples of an irreversible antagonist is aspirin. Aspirin irreversibly inhibits the enzyme cyclooxygenase, preventing the formation of prostaglandins and thromboxanes, thereby reducing inflammation and blood clotting.

Another example is phenoxybenzamine, used in the treatment of pheochromocytoma. It irreversibly binds to alpha-adrenergic receptors, preventing the effects of catecholamines like norepinephrine.

Clinical Significance

Irreversible antagonists have a long duration of action, as new receptors need to be synthesized to replace the inactivated ones. This makes them particularly useful in conditions that require a sustained effect. However, their irreversible action also means that any adverse effects cannot be quickly reversed, which can be a disadvantage in some situations.

See Also

• Pharmacology
• Reversible antagonist
• Competitive inhibition
• Non-competitive inhibition