Adrenergic Agonists
Introduction
- Adrenergic Agonists (Noradrenergic Agonists) are agents that stimulates/activates the adrenergic receptors (adrenoceptors) directly or indirectly.
- Adrenoceptors (Adrenergic receptors) are recognized into two families/classes on the basis of their responses to the adrenergic agonists epinephrine, norepinephrine, and isoproterenol.
– α-receptors (2 subtypes α1 & α2 based on their affinities for α agonists and blocking drugs)
– β-receptors (3 subtypes β1, β2 & β3 based on their affinities for adrenergic agonists and antagonists.)
Classification:
On the basis of therapeutic action, adrenergic agonists are classified as follows :-
1. Pressor Agents
- Pressor Agents are drugs which raises blood pressure.
- E.g.
– Nor-epinephrine /Nor-adrenaline
– Ephedrine
– Dopamine
– Phenylephrine
– Methoxamine
– Mephentermine
2. Cardiac Stimulants
- Cardiac stimulants are agents which raises cardiac output.
- E.g.
– Epinephrine / Adrenaline
– Dobutamine
– Isoprenaline / Isoproterenol (Rarely used)
3. Broncho-dilators
- Bronchodilators are agents that causes bronchodilation.
- E.g.
– Isoprenaline / Isoproterenol (Rarely used)
– Albuterol / Salbutamol
– Terbutaline
– Salmeterol
– Formoterol
– Bambuterol
– Levalbuterol
– Pirbuterol
– Arformoterol
4. Nasal Decongestants
- Nasal decongestants are agents which causes vasoconstriction.
- E.g.
– Phenylephrine
– Xylometazoline
– Oxymetazoline
– Naphazoline
– Pseudoephedrine
– Phenyl propanolamine
5. CNS Stimulants
- CNS stimulants are agents that triggers CNS.
- E.g.
– Amphetamine
– Dexamphetamine
– Methamphetamine
6. Anorectics
- Anorectics are agents which act as appetite suppressant.
- E.g.
– Fenfluramine
– Dexfenfluramine
– Sibutramine
7. Uterine relaxants
- Uterine relaxants are agents which relaxes uterine smooth muscles.
- E.g
– Ritodrine
– Isoxsuprine
8. Exclusive Drugs
- E.g
– Mirabegron – for treating overactive bladder
– Cocaine
– Clonidine
– Fenoldopam
– Methyldopa
On the basis of acting behavior, adrenergic agonists are classified as follows :-
1. Direct Acting
- Direct-acting agonists bind to adrenergic receptors on effector organs without interacting with the presynaptic neuron.
- As a group, these agents are widely used clinically.
- E.g. Most of adrenergic agonists
2. Indirect Acting
- Indirect-acting adrenergic agonists cause the release, inhibit the reuptake, or inhibit the degradation of epinephrine or norepinephrine i.e. act indirectly by enhancing release or blocking reuptake of norepinephrine or epinephrine.
- They potentiate the effects of epinephrine or norepinephrine produced endogenously, but do not directly affect postsynaptic receptors.
- E.g.
– Amphetamine
– Tyramine
– Cocaine etc.
3. Mixed acting
- Mixed acting agonists are agents that can stimulate adrenoceptors directly or indirectly.
- E.g.
– Ephedrine
– Pseudoephedrine
Catecholamines
– Epinephrine / Adrenaline
– Nor-epinephrine / Nor-adrenaline
– Dopamine
– Dobutamine
Therapeutic usage:
Adrenergic agonists may be used in following way:
- Used to treat bronchospasm; COPD, Asthma
- May be used for the treatment of type I hypersensitivity reactions (e.g. anaphylactic shock ).
- Used to prolong the action of local anesthetics.
- Used as a topical hemostatic agent on bleeding surfaces.
- used to treat shock, severe congestive heart failure, increase cardiac output
- Used as a mydriatic agent in eyes.
- Used as a pressor agent to treat hypotension.
- Used as Nasal decongestant
- Used for the relief of redness of the eyes associated with swimming, colds, and contact lenses.
- Used to treat overactive bladder.
- Used as an appetite suppressant.
- Used as uterine relaxant to delay premature labour.
