Antiadrenergic Drugs Sympatholytics Dr Nirbhay Kumar Asstt Professor

Anti-adrenergic Drugs (Sympatholytics) Dr. Nirbhay Kumar Asstt. Professor & Head Deptt. of Veterinary Pharmacology & Toxicology Bihar Veterinary College, Bihar Animal Sciences University, Patna

Anti-adrenergic Drugs (Sympatholytics) ü These are the drugs which antagonize the pharmacological action of sympathomimetic agents or alter the function of sympathetic nervous system inside the body.

Classification of Anti-adrenergic Drugs Antiadrenergic drugs can be classified under two heads: (1) Direct acting adrenergic receptor blockers or adrenergic antagonists: These drugs interact with adrenergic receptors and by occupying these sites do not allow an adrenergic agonist access to the receptor. (2) Indirect acting adrenergic neuron blockers: These drugs do not block receptors; instead, they act presynaptically at the nerve terminal to cause a decreased release of the endogenous neurotransmitter norepinephrine. The adrenergic neuron blockers interfere with the transmitter function of adrenergic neurons by the following mechanisms: i. By interfering with the synthesis of catecholamines: e. g. Methyldopa and methyltyrosine. ii. By interfering with storage of norepinephrine: e. g. Reserpine (It depletes NE stores in adrenergic neurons). iii. By preventing the release of norepinephrine: e. g. Guanethidine.

Classification of Anti-adrenergic Drugs

Pharmacological Actions of Sympatholytics 1. Heart: ü Heart rate, force of cardiac contraction and cardiac output decreases. ü The effect on a normal resting heart is not appreciable, but becomes prominent under sympathetic over-activity (exercise, vomition). 2. Blood Pressure: Epinephrine reversal (net result - hypotension). 3. Respiratory tract: Bronchoconstriction. 4. Skeletal muscles: Relaxation. 5. Eye: Reduces secretion of aqueous humour and intraocular tension. Thus, helpful in glaucoma.

Anti-adrenergic drugs and their Clinical Uses [I]. α Blockers:

Anti-adrenergic drugs and their Clinical Uses contd… [II]. β - Blockers: 1. Pronethalol: It was the first β blocker to be marketed. Although, effective in controlling arrhythmias and hypotension, it was found a carcinogen in mice and was later withdrawn. 2. Propranolol: It is a non-selective β (β 1+ β 2) antagonist. § The drug is a competitive antagonist of isoprenaline at β adrenoceptors. Useful in angina pectoris and protects the heart from sympathetic drive. § Inhibits the metabolic actions of adrenaline like muscle and liver glycogenolysis & lipolysis. § Bronchoconstrictor and antiarrhythmic for heart. 3. Acebutolol, Metoprolol, Atenolol: (Cardioselective β 1 blockers). § Used for – Angina pectoris, hypertension, cardiac arrhythmias etc.

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