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Adrenergic Blockers

Asmah Nasser, M.D. Adrenergic Blockers. Direct Adrenergic Antagonists. Alpha blockers Beta blockers Alpha plus beta blockers. Alpha Blockers (non-selective). Phenoxybenzamine (Non-competitive) Phentolamine (competitive) Ergot alkaloids: Ergotamine Ergotoxine. Phenoxybenzamine.

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Adrenergic Blockers

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  1. Asmah Nasser, M.D. Adrenergic Blockers

  2. Direct Adrenergic Antagonists • Alpha blockers • Beta blockers • Alpha plus beta blockers

  3. Alpha Blockers (non-selective) • Phenoxybenzamine (Non-competitive) • Phentolamine (competitive) • Ergot alkaloids: • Ergotamine • Ergotoxine

  4. Phenoxybenzamine • Non-competitive alpha adrenergic antagonist. • Net effect: α 1 blockage > α 2 blockage • Uses: malignant HTN, Pheochromocytoma, HTN 2° to Clonidine Withdrawal, Cheese Reaction

  5. Phentolamine • Non-selective Competitive Alpha Blocker • Used in HTN, Cocaine induced HTN. • Decreases the workload of the heart, and decreases the risk of MI

  6. Competitve Antagonist Vs. Non-competitive Antagonist

  7. Alpha selective Blockers • 1 selective: (ends with –sin or –cin) • Prazosin, • Terazosin • Doxazocin, • Tamsulocin • 2 selective: (inhibits Negative feedback) • Yohimbine

  8. Alpha 1 blockers • Effects: Blocks vaso- and aterioconstriction  vasodilation and arteriodilaton  Decrease in Blood pressure. • Blocks alpha receptors in the eye (pupillary dilator muscle)  Miosis • Reduces Bladder tone and allows for more motility (especially in patients with Urinary retention, BPH)

  9. Alpha 1 blockers Uses/Side effects • Drugs  Arteriodilation, used in Raynauld’s Phenomenon •  Increase Urinary Motility, used in Urinary rentention or BPH (Prazosin/Tamsulosin is most commonly used in BPH) • Side effects: Nasal Congestion, Hypotension

  10. 2 selective blockers • Yohimbine • Prevents Negative feedback  Increased Release of Epinephrine and Norepinephrine • Claimed to be an Aphrodisiac • Potential uses: Impotence, Co-administrated with drug induced sexual dysfuction

  11. Beta receptors on body Organs • Eyes: Beta receptors are found in the cillary epithelium in the eye. When stimulated  Produces Aqueous Humor. When blocked, decreases Aqueous Humor production • CVS: Beta 1 receptors are found in the heart. When stimulated  Increase in Heart rate • Pulm: Beta 2 receptors  Bronchodilation

  12. Beta blockers (1 selective) • Also known as Cardioselective Beta Blockers, decreases HR • Atenolol • Betaxolol • Esmolol (short half life) • Acebutalol • Metoprolol • ABEAM

  13. Beta Non-selective • Non Selective Beta blockers • Propranolol • Timolol • Pindolol • Blocks beta 1 and beta 2 recepors Bronchospasms and Decrease in HR • Contraindicated in Asthmatics • Decreases aqueous humor production  used in Open Angle glaucoma (Timolol)

  14. Uses of Beta Blockers • Hypertension - mild to moderate HTN • Angina pectoris -decreases cardiac work load • Cardiac arrhythmias • Myocardial infarction- prevents the reinfarction, prevents the development of ventricular fibrillation

  15. Uses of Beta Blockers • Glaucoma. Timolol is used • Migraine. Used for prophylaxis • Thyrotoxicosis • Essential tremors • Congestive cardiac failure (carvedilol and labetolol)

  16. Side effects of Beta blockers • Beta 2  Exacerbation of Asthma • Masks the sign of a hypoglycemic episode • Bradycardia

  17. Alpha and Beta Antagonists • Labetalol (doesn’t cross Placenta, also used in pregnancy) • Carvidilol • Blocks alpha receptors  Decrease BP • Blocks beta receptors  Decreases HR • Used in Severe HTN, Angina

  18. Questions • What drugs can be given in HTN in pregnancy? • Which is given orally (For home dosing)? • Which is given IV (for immediate tx)?

  19. Indirect Adrenergic Antagonist • Resperpine • MOA: Prevents Storage of NE, allowing more MAO to metabolism NE/dopamine. Uses: HTN • Crosses BBB • Side effects: Depression, Suicidal Ideations

  20. Pretest Questions The nonselective β-adrenergic blocking agent that is also a competitive antagonist at α1-adrenoceptors is • a. Timolol • b. Nadolol • c. Pindolol • d. Acebutolol • e. Labetalol

  21. Pretest Questions Epineprhine =X When combined with an antagonist (IC or INC), a shift in the dose response curve occurs. The curve labeled X + INC would most likely occur when vascular smooth muscle is treated with NE in the presence of: a. Terazosin b. Phentolamine c. Labetalol d. Phenoxybenzamine e. Prazosin

  22. Pretest Questions • A predictably dangerous side effect of nadolol that constitutes a contraindication to its clinical use in susceptible patients is the induction of • a. Hypertension • b. Cardiac arrhythmia • c. Asthmatic attacks • d. Respiratory depression • e. Hypersensitivity

  23. Pretest Questions • All of the following drugs are used topically in the treatment of chronic wide-angle glaucoma. Which of these agents reduces intraocular pressure by decreasing the formation of the aqueous humor? • a. Timolol • b. Echothiophate • c. Pilocarpine • d. Isofluorphate • e. Physostigmine

  24. Pretest Questions • Both phentolamine and prazosin • a. Are competitive antagonists at α1-adrenergic receptors • b. Have potent direct vasodilator actions on vascular smooth muscle • c. Enhance gastric acid secretion through a histamine-like effect • d. Cause hypotension and bradycardia • e. Are used chronically for the treatment of primary hypotension

  25. Pretest Questions • A 58-year-old male with angina is treated with atenolol. Select the mechanism of action of atenolol. • a. α-adrenergic agonist • b. α-adrenergic antagonist • c. β-adrenergic agonist • d. β-adrenergic antagonist • e. Mixed α and β agonist • f. Mixed α and β antagonist

  26. Pretest Questions • A 75-year-old female with CHF is treated with carvedilol. Select the mechanism of action of carvedilol. • a. α-adrenergic agonist • b. α-adrenergic antagonist • c. β-adrenergic agonist • d. β-adrenergic antagonist • e. Mixed α and β agonist • f. Mixed α and β antagonist

  27. Pretest Questions • A 35-year-old male with a pheochromocytoma is treated with labetalol. Select the mechanism of action of labetalol. • a. α-adrenergic agonist • b. α-adrenergic antagonist • c. β-adrenergic agonist • d. β-adrenergic antagonist • e. Mixed α and β agonist • f. Mixed α and β antagonist

  28. Pretest Questions • A 65-year-old male has a blood pressure of 170/105 mmHg. Which of the following would be effective in lowering this patient’s blood pressure? • a. Methylphenidate • b. Terbutaline • c. Dobutamine • d. Pancuronium • e. Prazosin • f. Scopalamine

  29. Pretest Questions • Which of the following agents might mask the hypoglycemia in treated diabetics? • a. An α-adrenergic agonist • b. An α-adrenergic antagonist • c. A β-adrenergic agonist • d. A β-adrenergic antagonist • e. A cholinergic agonist • f. A cholinergic antagonist

  30. Pretest Questions • Which of the following occurs in the treatment of glaucoma with a β-adrenergic antagonist? • a. Decreased aqueous humor secretion • b. Pupillary dilator muscle fiber contraction • c. Dilation of the uveoscleral veins • d. Direct opening of the trabecular meshwork • e. Circular pupillary constrictor muscle contraction

  31. Pretest Questions • A 66-year-old male with a one-year history of essential hypertension has minimal response to diet and a diuretic. His blood pressure is now 160/105 mmHg. The diuretic is discontinued, and propranolol is given. • a. α-adrenergic antagonist • b. β-adrenergic antagonist • c. Calcium (Ca) channel antagonist • d. Carbonic anhydrase inhibitor • e. Histamine (H1) receptor antagonist • f. H2 receptor antagonist • g. MAOI

  32. Pretest Questions • Which drug is used in pheochromocytoma? • a. Pilocarpine • b. Methylphenidate • c. Propranolol • d. Ritodrine • e. Phenoxybenzamine

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