General Classification of Adrenergic Agonists

GENERAL CLASSIFICATION OF ADRENERIGIC AGONISTS

Adrenergic agents are divided into three classes

I. Direct-acting adrenergic agonists

They bind to and activate α1 , α2 , β1 , and β2 receptors. Naturally occurring molecules, which bind to these receptors include NE (a neurotransmitter which binds to α1 , α1 , and β1 receptors), Epinephrine (a hormone produced in and secreted from the adrenal medulla, which binds to α1 , α2 , β1 , and β2 receptors, it is a nonselective adrenergic agonists), and Dopamine (also a neurotransmitter, which binds to α1 , α2 , and β1 receptors).

Examples of drugs: xylometazoline, phenylephrine, methoxamine.

II. Indirect-acting adrenergic agonists

They produce NE-like actions by stimulating NE release and preventing its reuptake and produces activation.

Example: Tyramine.

III. Dual-acting adrenergic agonists

These agents act as direct and indirect adrenergic agonists (hence, dual-acting). They bind to adrenergic receptors and stimulate NE release.

Examples: Ephedrine, Amphetamine, Mephenteramine.

Classifications Based on Therapeutic Uses

Adrenergic drugs used for raising blood pressure (vaso-constrictors): Noradrenaline, Metaraminol 

Drugs used for their ionotropic action on the heart: Dopamine, Dobutamine, Xamoterol

Drugs used as central stimulants: Amphetamine (Benzedrine)

Drugs used as smooth muscle relaxants: Adrenaline (epinephrine), Isoprenaline, Isoxsuprine Selective β2 stimulant: Salbutamol

Drugs used in allergic reactions: Adrenaline, Ephedrine

Drugs used as local vaso-constrictors: Adrenaline, Phenylephrine, Naphazoline 

Drugs used for suppressing the appetite: Fenfluramine, Phenteramine, Amphetamine

Classification Based on Chemical Structures

1. Catecholamines

Compounds with hydroxyl (–OH) substitution in the third and fourth position of the benzene ring are termed as catecholamines.

II. Noncatecholamines

Those compounds that lack the hydroxyl at third and fourth position of the benzene ring are noncatecholamines. They release noradrenaline or dopamine from the sympathetic neurons. This indirect action produces effects mainly resembling those of externally administered noradrenaline.