Adrenergic drugs : Uses and classification

Adrenergic drugs Drugs that produce similar effects to those produced by sympathetic nervous system or adrenergic system thus they are also called sympathomimetic drugs. Adrenergic system’s main function is to prepare the body for fight and flight. In stress it increases heart rate , cardiac output and stroke volume.

It shifts blood from skin, gut, kidney to heart , muscle, brain and lungs

Neurotransmitter

Neurotransmitters of Adrenergic systems are :

• Noradrenaline
• Dopamine
• adrenaline

Receptors of adrenergic systems

Adrenergic system has two receptors types :

1. Alpha receptor
2. Beta receptor

1. Alpha receptor :
   1. 𝛂1 : 𝛂1A,𝛂1B and 𝛂1D
   2. 𝛂2 : 𝛂2A,𝛂2B and 𝛂2C
2. Beta receptor :
   1. 𝛃: 𝛃1 ,𝛃2 and 𝛃3

Characteristics of Adrenergic receptors :

1. 𝛃1 receptor :
   1. LOC : Heart
   2. Agonist : dobutamine
   3. Antagonist : metoprolol,atenolol
   4. Response : Increase heart rate and force of contraction

2. 𝛃2 receptor :
   1. LOC : Smooth muscle , vascular , bronchial , gut
   2. Agonist : salbutamol
   3. Antagonist : butoxamine
   4. Response : relaxation

3. 𝛃3 receptor :
   1. LOC : adipose tissue
   2. Agonist : mirabegron
   3. Response : lipolysis

4. 𝛂1 receptor :
   1. LOC : post junctional effector organ
   2. Agonist : phenylephrine
   3. Antagonist : prazosin
   4. Response : contraction, relaxation, contraction, increase DAG and IP3

5. 𝛂2 Receptor :
   1. LOC : prejunctional nerve ending
   2. Agonist : clonidine
   3. Antagonist : yohimbine
   4. Response : decrease insulin release,decrease NE release, glycogenolysis

Depending on mode of action :

1. Direct acting sympathomimetics:

Direct act as agonist on alpha , beta or on both receptors

1. NA
2. Isoprenaline
3. Salbutamol
4. Dopmine

2. Indirect acting sympathomimetics:

Act on an adrenergic neuron to release NA.

1. Tyramine
2. Amphetamine

3.mixed acting sympathomimetics :

Work as both

1. Ephadrine

Clinical Classification

1. Vasopressor : Dopamine,methoxamine
2. Cardiac stimulant : adrenaline, dopamine,isoprenaline
3. CNS stimulants : amphetamine,ephedrine
4. Bronchodilators : Adrenaline, salbutamol, isoprenaline
5. Nasal decongestants : ephedrine, oxymetazoline
6. Appetite suppressants : fenfluramine
7. Uterine relaxants : salbutamol, ritodrine

Chemical classification

1. Catecholamine :
   1. Non adrenaline
   2. Adrenaline
   3. Dopamine
2. Noncatecholamine :
   1. Isoprenaline
   2. Dopamine

Pharmacological action

1. Heart :
   1. Increase heart rate
   2. Increase BP
   3. Increase contraction
   4. Increase pacemaker activity
2. Blood vessel:
   1. Vasodilation
   2. Vasoconstriction
3. B.P. :
   1. N.A. = increase systolic, diastolic
   2. Isoprenaline = increase systolic, diastolic
   3. Adrenaline ( IV ) = increase systolic, diastolic
4. Bronchodilators
5. Eye :
   1. Intraocular pressure decrease
6. GIT :
   1. Gut relaxant
7. Uterus :
   1. At pregnancy relaxation
8. CNS :
   1. Tremor may occur