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Sympatholytics

Adrenergic blocking agents, also known as adrenergic antagonists, block alpha and/or beta receptor sites and have the opposite effect of adrenergic agents. They are classified based on the type of adrenergic receptor they block, including alpha1, alpha2, beta1, beta2, and beta3 receptors. Common uses include treatment of hypertension, heart failure, and benign prostatic hyperplasia. Side effects may include hypotension, tachycardia, and bronchospasm.

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 Have the opposite effect of adrenergic agents  Also known as ◦ adrenergic antagonists or ◦ adrenergic Blocking Agents
Receptor Location Mechanism followed Alpha 1 Blader, radial muscle of eye, blood vessels Gq cause constriction Alpha 2 Smooth muscles Gi relaxation Beta 1 SA, AV node, heart Gs Increase heart rate Beta 2 Blood vessels , liver, smooth muscles Gs relaxation Beta 3 lipocytes Gs
◦ Synthesis of NE ◦ Storage of NE in vesicles ◦ Release of NE ◦ Binding to receptors ◦ Uptake mechanism ◦ Function ◦ Metabolism ◦ Excretion
Classified by the type of adrenergic receptor they block  Alpha1 and alpha2 receptors  Beta1 and beta2 and beta 3 receptors
Phenoxybenzamine Block alpha 1 and alpha 2 by linking covalently Non selective block alpha 1 and alpha 2 Block is irreversibly and new receptors are made
CVS Vasodilatation – arteriolar and venous  BP Magnitude dependent on symp. activity at that time More in erect that in supine position – postural hypotension More marked if hypovolaemia is present Baroreflex activation – reflex tachycardia – tends to oppose the fall by  HR and CO
OTHER EFFECT ↓contraction of trigone and sphincter in blood vessels  urine flow insulin secretion from islet cells (2 blockers) Miosis Nasal stuffiness  adrenergic sweating
α1 – blockers : Clinical uses Reduce blood pressure Hypertensive emergencies Long term treatment Phaeochromocytoma Vasodilatation Peripheral vascular insufficiency To reverse vasoconstrictor excess Improve urine flow Benign prostatic hyperplasia
α1 – blockers : Adverse effects •Postural hypotension ( less with α1 selective - venodilatation is less) •Reflex tachycardia ( less with α1 selective) •Salt and water retention •Nasal stuffiness •Miosis •Failure of ejaculation
Ergot alkaloids (ergotamine): Partial agonist & blocking property Also affect other receptors (eg. 5-HT, ) Therapeutic effects (migraine, uterus) not related to  blockade. Uses: Migraine (acute attack) Uterotonic – (methylergonovine) in PPH
Phenoxybenzamine: 1 > 2 ; Irreversible : Covalent binding with receptor Long duration of action (14 - 48 hrs) Also blocks 5-HT, ACh & H1 receptors Inhibits neuronal & extra-neuronal uptake of NA Absorbed from GIT, low bioavailability
Clinical use: Phaeochromocytoma Control of BP Prior to surgery Adverse effects: Postural hypotension, Tachycardia, Nasal stuffiness,  ejaculation Phenoxybenzamine
Phentolamine : 1 = 2  PVR –  blockade + direct (non adrenergic)  HR – Reflex + 2 presynaptic on cardiac symp. terminals Poorly absorbed orally Clinical use: Phaeochromocytoma Local vasoconstrictor excess Adverse effects: Cardiac stimulation : - tachycardia, arrhythmia, angina GIT Stimulation : diarrhoea;  gastric acid secretion
Tolazoline: Similar to phentolamine Slightly less potent Better absorption from GIT Rapidly excreted in urine Limited clinical application: peripheral vasospastic disease
1 Selective Agents Prazosin & Terazosin: 1 >>>> 2 Effective in management of hypertension Low affinity for 2 Relative absence of tachycardia ↓ Triglycerides & LDL, ↑ HDL (favourable) Both are extensively metabolized by liver Prazosin shows high 1st Pass effect (50%) Oral absorption - good Terazosin :Bioavailability >90%; >18 h action Uses: Hypertension and BPH Adverse effects First dose effect Postural hypotension Salt & water retention ( long term use)
Tamsulosin Selective α1 anatgonist Has greater selectivity for α1A subtype Has greater efficacy for BPH Relatively smaller effects on blood vessels Doxazosin: Similar to Prazosin but longer t ½ (22 Hr) Alfuzosin : similar to prazosin
Clinical Uses Of  Blockers •Pheochromocytoma •Hypertensive emergencies •Chronic hypertension – non selective blockers are not used •Peripheral vascular diaease – spastic (Raynauds), not morphological •Local vasoconstrictor excess – phentolamine useful- local infiltration •Urinary obstruction – BPH – prazosin, terazosin, tamsulosin •CHF α2- selective antagonists do not have any recognised clinical use
 Block alpha & beta receptor sites (nonselective)  direct or indirect acting on the release of norepinephrine and epinephrine  Use - Cardiac arrthymias (HR), HTN ( cardiac output), angina (O2 demand)  SE - CHF, bronchospasm, bradycardia, wheezing
 Competative agonist  Propanolol  Acetabutol
 Sympatholytic 1 adrenergic antagonist Class II antiarrhytmic  Antihypertensive Antianginal Bronchoconstrictor  Symptoms of overdose include extreme bradycardia, advanced atrioventricular block, intraventricular conduction defects, hypotension, severe congestive heart failure, seizures, and in susceptible patients, bronchospasm, and hypoglycemia
 Sympatholytic 1 adrenergic antagonist  Antihypertensive Antiarrhythmic Antianginal Bronchoconstrictor  Symptoms of an atenolol overdose include a slow heart beat, shortness of breath, fainting, dizziness, weakness, confusion, nause a, and vomiting
 Sympatholytic 1 adrenergic antagonist  Antihypertensive Glaucoma medication Bronchoconstrictor  Predicted symptoms of overdose include bradycardia, congestive heart failure, hypotension, bronchospasm, and hypoglycemia.
 Sympatholytic  adrenergic antagonist  Treatment for heart failure  Not expected to be toxic following ingestion.
 Sympatholytic  adrenergic antagonist  Bronchoconstrictor
 Sympatholytic 1 adrenergic antagonist  Antihypertensive Heart failure medication Bronchoconstrictor
 Sympatholytic  adrenergic antagonist  Antihypertensive  Symptoms of overdose include abdominal irritation, central nervous system depression, coma, extremely slow heartbeat, heart failure, lethargy, low blood pressure, and wheezing
 Sympatholytic  adrenergic antagonist  Antihypertensive Bronchoconstrictor  Symptoms of overdose include drowsiness, vertigo, headache, and atriventricular block.
 www. wikipedia.com  www. cvpharmacology.com  www.about-pharmacology.com  Goodman & Gilman’s the pharmacological basis of therapeutics 12th edition  Modern pharmacology with clinical applications by Charles R.Craig, Robert E.Stitzel 5th edition  Textbook of medical physiology 11th edition by Guyton & Hall
Sympatholytics