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Sympatholytic & adrenergic blockers  -receptor Antagonists

Sympatholytic & adrenergic blockers  -receptor Antagonists. Prof. Hanan Hagar Dr. Ishfaq Bukhari Pharmacology Unit College of Medicine. Adrenergic Neuron Blockers. Adrenoceptor Blockers. Alpha & beta- adrenergic receptor blockers. Classification of sympatholytics.

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Sympatholytic & adrenergic blockers  -receptor Antagonists

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  1. Sympatholytic & adrenergic blockers-receptor Antagonists Prof. Hanan Hagar Dr. Ishfaq Bukhari Pharmacology Unit College of Medicine

  2. Adrenergic Neuron Blockers Adrenoceptor Blockers Alpha & beta- adrenergic receptor blockers

  3. Classification of sympatholytics • Adrenergic neuron blockers • Formation of False Transmitters e.g. a-Methyl dopa • Depletion of Storage sites e.g. reserpine • Inhibition of release & enhance uptake e.g. guanethidine • Stimulation of presynaptic a2receptors e.g. clonidine and a-Methyl dopa • Adrenergic receptor blockers

  4. Classification of sympatholytics a-Methyl dopa • Forms false transmitter that is released instead of NE • Acts centrallyas a2 receptor agonist to inhibit NE release • Drug of choice in the treatment of hypertension in pregnancy (pre-eclampsia - gestational hypertension). Clonidine • Acts directly as a2 receptor agonist to inhibit NE release • suppresses sympathetic outflow activity from the brain. • Little Used as Antihypertensive agent due to rebound hypertension upon abrupt withdrawal. • Apraclonidineis used in open angle glaucoma as eye drops. acts by decreasing aqueous humor formation.

  5. 1. Adrenergic Neuron Blockers [SYMPATHOLYTICS] 1. METHYLDOPA a-methyl tyrosine Na Norepinephrine (NE) Tyrosine False Transmitters Dopa Tyrosine  Antihypertensive in PREGNANCY DA 2. RESERPINE NE Depletes Stores Methyl-NE works as false transmitter a2 NET 4. Clonidine Presynaptic a2agonist 3. Gaunthidine  Inhibit Release  Enhance Uptake 2. Adrenoceptor Blockers [ADRENOLYTICS] b2 COMT b1 a1

  6. Adrenergic receptor blockers Adrenergic receptor blockers or adrenolytics They block sympathetic actions by antagonizing • -receptor antagonists or • B-receptor antagonists

  7. Classification of -receptor Antagonists Non-selective antagonists e.g. phenoxybenzamine & phentolamine. 1-selective antagonists e.g. prazosin, doxazosin. 2-selective antagonists e.g. yohimbine

  8. Non-Selective - Adrenoceptor Antagonists Phentolamine: reversible blocking of 1 & 2 receptors. Short acting (4 hrs). Phenoxybenzamine: Irreversiblblock of both 1 and 2receptors Long-acting (24 hrs).

  9. Both drugs cause: • Postural hypotension. • Decrease peripheral vascular resistance • Increase cardiac output (α2 block). • Reflex tachycardia. • Both drugs can precipitatearrhythmias and angina and are contra-indicated in: patients with decreased coronaryperfusion.

  10. Reflex tachycardia due to the fall in B.P, mediated by baroreceptor reflex and due to block 2-presynaptic receptors in the heart. Therapeutic Uses: • Pheochromocytoma: Before surgical removal to protect against hypertensive crisis.

  11. Adverse Effects of non-Selective - Adrenoceptor Antagonists : • Postural hypotension • Tachycardia • Headache • Nasal stuffiness or congestion • Vertigo & drowsiness • Male sexual dysfunction (inhibits ejaculation).

  12. Selective 1- Antagonists Prazosin &doxazosin. Prazosin(short half-life) Doxazosin, terazosin (long half life ) 1–antagonists cause : • Vasodilatation due to relaxation of arterial and venous smooth muscles • Fall in arterial pressure with less tachycardia than with non-selective blockers

  13. Therapeutic Uses: • Benign prostatic hyperplasia. • Treatment of hypertension with prostate enlargement. • Reynaud's disease (vasospasm) • (Reynaud's disease causes some areas of your body — such as your fingers and toes — to feel numb and cold in response to cold temperatures or stress).

  14. Selective 1A–antagonist Tamsulosin (Uroselective) • a selective 1A–antagonist. • 1A receptors present in prostate • Tamsulosinis used in treatment of benign prostatic hypertrophy (BPH). • Tamsulosin produce: relaxation of smooth muscles of bladder neck & prostate →improve urine flow. • Has minimal effect on blood pressure.

  15. Selective 1A–antagonist Tamsulosin Tamsulosin Relaxation of bladder neck can improve urine flow Adverse effects of 1- Antagonists as before with non selective but to a lesser degree BPH

  16. 2-selective antagonists • e.g. yohimbine • Used as aphrodisiac (increases libido) in the treatment of erectile dysfunction. • Increase nitric oxide released in the corpus cavernosum thus producing vasodilator action and contributing to the erectile process.

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