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Sympatholytics
Sympatholytics, also known as adrenergic antagonists or blocking agents, work in opposition to adrenergic agents by blocking alpha and beta receptor sites. They are classified based on the type of adrenergic receptor they block, including alpha1, alpha2, beta1, beta2, and beta3 receptors. Common alpha blockers include phenoxybenzamine, ergot alkaloids, phentolamine, tolazoline, prazosin, terazosin, doxazosin, and tamsulosin. Common beta blockers mentioned include propanolol, acetabutolol, atenolol, betaxolol, carvedilol, metoprol
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Sympatholytics
- 1.
- 2. Sympatholytics Have the oppositeeffect of adrenergic agents Also known as Adrenergic antagonists or Adrenergic blocking agents
- 3. Synthesis ofNE Storage of NE in vesicles Release of NE Binding to receptors Uptake mechanism Function Metabolism Excretion Neurotransmission at adrenergic neurons
- 4. Classified by thetype of adrenergic receptor they block Alpha1 and alpha2 receptors Beta1 and beta2 and beta 3 receptors Classification of Sympatholytics
- 5. Phenoxybenzamine Block alpha1 and alpha 2 by linking covalently Non selective block alpha 1 and alpha 2 Block is irreversibly and new receptors are made Alpha blockers
- 6. CVS Vasodilatation – arteriolarand 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
- 7. OTHER EFFECT contraction oftrigone and sphincterin blood vessels urine flow insulin secretion from islet cells(α2 blockers) Miosis Nasal stuffiness adrenergic sweating
- 8. 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
- 9. α1 – blockers: Adverse effects •Postural hypotension ( less with α1 selective - vesodilatation is less) •Reflex tachycardia ( less with α1 selective) •Salt and water retention •Nasal stuffiness •Miosis •Failure of ejaculation
- 10. Ergot alkaloids (ergotamine): Partial agonist & blocking property Also affect other receptors (eg. 5-HT, ) Therapeutic effects (migraine, uterus) not related to alpha blockade. Uses: Migraine (acute attack) Uterotonic – (methylergonovine) in PPH
- 11. Phenoxybenzamine: α1 >α2 ; 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
- 12. Phenoxybenzamine Clinical use: Phaeochromocytoma Control ofBP Prior to surgery Adverse effects: Postural hypotension, Tachycardia, Nasal stuffiness, Ejaculation
- 13. Phentolamine : α1= α 2 PVR – blockade + direct (non adrenergic) HR – Reflex + α 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
- 14. Tolazoline: Similar to phentolamine Slightlyless potent Better absorption from GIT Rapidly excreted in urine Limited clinical application: Peripheral vasospastic disease
- 15. α1 Selective Agents Prazosin& Terazosin: α1 >>>> α2 Effective in management of hypertension Low affinity for α2 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)
- 16. Doxazosin: Similar to Prazosinbut longer t1/2 (22Hr) Alfuzosin: Similar to prazocin Tamsulosin Selective α1 antagonist Has greater selectivity for α1A subtype Has greater efficacy for BPH Relatively smaller effects on blood
- 17. Clinical Uses Ofα Blockers •Phaeochromocytoma •Hypertensive emergencies •Chronic hypertension – non selective blockers are not used •Peripheral vascular disease – 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
- 18. Adrenergic Blockers (antagonists/ sympatholytics) Block alpha & beta receptor sites(non selective) Direct or indirect acting on the release of norepinephrine and epinephrine Use - Cardiac arrhythmias (HR), HTN (cardiac output), angina (O2 demand) SE - CHF, bronchospasm, bradycardia, wheezing
- 19. Beta blockers Competitiveagonist Propanolol Acetabutaol
- 20. Acetabutolol Sympatholytic β1adrenergic antagonist Class II antiarrhythmic 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 hypoglycaemia
- 21. Atenolol Sympatholytic β1adrenergic antagonist Antihypertensive Antiarrhythmic Antianginal Bronchoconstrictor Symptoms of an atenolol overdose include a slow heartbeat, shortness of breath, fainting, dizziness, weakness, confusion, nausea, and vomiting
- 22. Betaxolol Sympatholytic β1adrenergic antagonist Antihypertensive Glaucoma medication Bronchoconstrictor Predicted symptoms of overdose include bradycardia, congestive heart failure, hypotension, bronchospasm, and hypoglycaemia.
- 23. Carvedilol Sympatholytic βadrenergicantagonist Treatment for heart failure Not expected to be toxic following ingestion.
- 24. Metipranolol Sympatholytic βadrenergic antagonist Bronchoconstrictor
- 25. Metoprolol Sympatholytic β1adrenergic antagonist Antihypertensive Heart failure medication Bronchoconstrictor
- 26. Nadolol Sympatholytic βadrenergic antagonist Antihypertensive Symptoms of overdose include abdominal irritation, central nervous system, depression, coma, extremely slow heartbeat, heart failure, lethargy, low blood pressure, and wheezing
- 27. Penbutolol Sympatholytic βadrenergic antagonist Antihypertensive Bronchoconstrictor Symptoms of overdose include drowsiness, vertigo, headache, and atrioventricular block.