Classification Of Sympathomimetics Or Adrenergic Drugs

Classification Of Sympathomimetics Or Adrenergic Drugs

Question 1. Classify Sympathomimetics. Write Contraindication And Therapeutic Uses Of Adrenaline. Add A Short Note On the Adrenaline And Lignocaine Combination.
Answer:

Classification Of Sympathomimetics Or Adrenergic Drugs

1. On The Basis of their Mechanism of Action

• Direct-acting sympathomimetics: They act directly as agonists on α and/or β adrenoreceptors, for Example. are adrenaline, noradrenaline, isoprenaline, phenylephrine, methoxamine, xylometazoline, salbutamol, and many more
• Indirect-acting sympathomimetics: They act on adrenergic neurons to release noradrenaline which then acts on the adrenoreceptors, for Example. tyramine and amphetamine
• Mixed-action sympathomimetics: They act directly as well as indirectly, for Example. ephedrine, amphetamine, mephentermine

2. On the Basis of their Chemical Structure

• Catecholamines: Sympathomimetics with catechol nuclei are called catecholamines, for Example. adrenaline, noradrenaline,
• Non-catecholamines: Sympathomimetics that lack catechol nuclei are called non-catecholamines, for Example, tyramines, ephedrine, amphetamine, phenylephrine, salbutamol, etc.

Classification of Sympathomimetics or Adrenergic Drugs

3. Classification of Adrenergic Drugs Based on Their Therapeutic Uses

• Pressor Agents: Noradrenaline, Phenylephrine, Ephedrine, Dopamine, Methoxamine, Mephentermine.
• Cardiac Stimulants: Adrenaline, Dobutamine, Isoprenaline
• Bronchodilators: Isoprenaline, Salbutamol, Salmeterol, Formoterol, Bambuterol
• Nasal Decongestants: Phenylephrine, Naphazoline, Xylometazoline, Oxymetazoline, Pseudoephedrine
• CNS Stimulants: Amphetamine, Methamphetamine, Dexamphetamine
• Anorectics: Fenflramine, Sibutramine, Dexfenflramine
• Uterine relaxants and vasodilators: Ritodrine, Salbutamol, Isoxsuprine, Terbutaline.

Therapeutic Uses Of Adrenaline

• Anaphylactic shock: Adrenaline acts as a life-saving drug in anaphylactic shock and also in Type I hypersensitivity reaction. It should be given as 0.3 to 0.5  ml of 1:1000 solution and is given IM.
• Allergy: It reverses the manifestations of allergic disorders.
• Adrenaline along with the lignocaine due to its vasoconstrictor effect causes late absorption of local anesthetic and prolongs the duration of local anesthesia.
• Bronchial asthma: Adrenaline acts as a powerful bronchodilator in bronchial asthma. It is very useful during acute attacks. It should be given 0.3 to 0.5 ml of 1:1000 solution SC
• Hemostatic: Adrenaline acts as a local hemostatic for the control of bleeding from tooth extraction and also in various other surgical procedures.
• Cardiac arrest: Adrenaline is used in the treatment of cardiac arrest which happens due to drowning or electrocution. Adrenaline is given IV in 1:10000 concentration with other supportive measures.
• Glaucoma: Adrenaline is used in glaucoma as it shows poor penetration when it is applied locally in the eye, so it should be given as a prodrug.

Contraindications Of Adrenaline

• Adrenaline is contraindicated in hypertensive, hyperthyroid, and in angina patients.
• Adrenaline mixed with the local anesthetic should be used very cautiously for dental anesthesia in patients with heart disease.
• It should not be given during anesthesia with halothane.
• Patients receiving beta-blockers can cause hypertensive crisis and cerebral hemorrhage due to their unopposed action on vascular alpha-1 receptors.

Sympathomimetics Drugs: Types, Mechanisms, and Examples

Adrenaline And Lignocaine Combination

Adrenaline is added to lignocaine because of the following reasons:

1. Infiltration block: The duration of action of lignocaine is proportional to the time of contact with the nerve.
When lignocaine is infiltrated around the injury site (by subcutaneous route), some of it may enter the subcutaneous blood vessels. It has two implications:

• Lignocaine goes away from the nerves of the injury site. Thus, its action quickly diminishes.
• The lignocaine which has entered the blood vessel may go to the heart and brain causing systemic toxicity, i.e. cardiotoxicity and neurotoxicity.

 

 

The addition of adrenaline cause vasoconstriction and thus lignocaine is not able to enter the blood vessels resulting in:

• Prolongation of the duration of action
• Less systemic toxicity
• Adrenaline provides a bloodless field for surgery.

2. Spinal anesthesia: Adrenaline is added to lignocaine for spinal anesthesia to increase the duration and intensity of the block. It acts by:

• Decreasing the spinal blood flow may reduce the clearance of lignocaine from CSF
• Acting on the α2A; receptors, it may reduce the tiring of neurons and inhibit the release of pain mediators like substance P or neurokinin-1.

Question 2. Enumerate Three Indications For The Use Of Adrenaline.
Answer:

Following are the three indications for the use of adrenaline:

1. Anaphylactic shock: Adrenaline acts as a life-saving drug in anaphylactic shock and also in Type I hypersensitivity reaction. It should be given as 0.3 to 0.5 ml of 1:1000 solution and is given IM.
2. Allergy: It reverses the manifestations of allergic disorders.
3. Bronchial asthma: Adrenaline acts as a powerful bronchodilator in bronchial asthma. It is very useful during acute attacks. It should be given 0.3 to 0.5 ml of 1:1000 solution SC.