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Chapter 18

Chapter 18. Adrenergic Antagonists. Adrenergic Antagonists. Cause direct blockade of adrenergic receptors With one exception, all produce reversible (competitive) blockade Most adrenergic antagonists are more selective than the adrenergic agonists. Two major groups

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Chapter 18

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  1. Chapter 18 Adrenergic Antagonists

  2. Adrenergic Antagonists • Cause direct blockade of adrenergic receptors • With one exception, all produce reversible (competitive) blockade • Most adrenergic antagonists are more selective than the adrenergic agonists. • Two major groups • Alpha-adrenergic blocking agents • Beta-adrenergic blocking agents

  3. Adrenergic Antagonists • Alpha-adrenergic antagonists I:therapeutic and adverse response to alpha blockade • Alpha-adrenergic antagonists II:properties of individual alpha blockers • Beta-adrenergic antagonists I:therapeutic and adverse responses to beta blockade • Beta-adrenergic antagonists II:properties of individual beta blockers

  4. Therapeutic Applications of Alpha Blockade • Essential hypertension • Lowers blood pressure by blocking alpha1 receptors on arterioles and veins, causing vasodilation • Reversal of toxicity from alpha1 agonists • Benign prostatic hyperplasia • Reduced contraction of smooth muscle in the bladder neck and prostatic capsule

  5. Therapeutic Applications of Alpha Blockade • Pheochromocytoma • Catecholamine-secreting tumor • Usually located in adrenal medulla • Principal cause of hypertension is usually activation of alpha1 receptors, but beta1 receptors can also contribute • Treatment: best option is surgery • Inoperable tumor: alpha1 antagonists suppress hypertension • Surgery: before surgery, manipulation of tumor can cause massive catecholamine release

  6. Therapeutic Applications of Alpha Blockade • Raynaud’s disease • Peripheral vascular disorder • Vasospasms in the toes and fingers • Suppress symptoms by preventing alpha-mediated vasoconstriction • Ineffective against other peripheral vascular disorders that involve inappropriate vasoconstriction

  7. Adverse Effects of Alpha1 Blockade • Detrimental effects result from blockade of alpha1 receptors • Effects from alpha2 receptors are minor • Orthostatic hypotension • Blockade of alpha receptors on veins • Reduced muscle tone in the venous wall • Upon standing, blood pools in the veins • Return of blood to the heart reduced • Cardiac output decreased: blood pressure drops

  8. Adverse Effects of Alpha1 Blockade • Reflex tachycardia • Reflex to increase heart rate via the autonomic nervous system (ANS) • Nasal congestion • Dilates the blood vessels of the nasal mucosa • Inhibition of ejaculation • Alpha1 activation required for ejaculation • Impotence is reversible; resolves when drug is discontinued • Sodium retention and increased blood volume • Reduced BP promotes renal retention of sodium and water • Usually combined with diuretic when used for hypertension

  9. Adverse Effects of Alpha2 Blockade • The most significant adverse effect associated with alpha2 blockade—potentiation of the reflex tachycardia

  10. Alpha-Adrenergic Antagonists II • Prazosin • Terazosin • Doxazosin • Tamsulosin • Alfuzosin • Phentolamine • Phenoxybenzamine

  11. Prazosin • Actions and uses • Pharmacokinetics • Adverse effects • Preparations, dosage, and administration

  12. Terazosin • Actions and uses • Pharmacokinetics • Adverse effects • Preparations, dosage, and administration

  13. Doxazosin • Actions and uses • Pharmacokinetics • Adverse effects • Preparations, dosage, and administration

  14. Tamsulosin • Actions and uses • Pharmacokinetics • Adverse effects • Drug interactions • Preparations, dosage, and administration

  15. Alfuzosin • Actions and uses • Pharmacokinetics • Adverse effects • Drug interactions • Preparations, dosage, and administration

  16. Phentolamine • Actions and uses • Adverse effects • Preparations, dosage, and administration

  17. Phenoxybenzamine • Actions and uses • Adverse effects • Preparations, dosage, and administration

  18. Beta-Adrenergic Antagonists I • Therapeutic applications of beta blockade • Angina pectoris • Hypertension • Cardiac dysrhythmias • Myocardial infarction • Heart failure • Hyperthyroidism • Migraine • Stage fright • Pheochromocytoma • Glaucoma

  19. Beta-Adrenergic Antagonists I • Adverse effects of beta blockade • Adverse effects involve both beta1 and beta2 blockade.

  20. Beta-Adrenergic Antagonists I • Adverse effects of beta1 blockade • Bradycardia • Reduced cardiac output • Precipitation of heart failure • AV heart block • Rebound cardiac excitation

  21. Beta-Adrenergic Antagonists I • Adverse effects of beta2 blockade • Bronchoconstriction • Inhibition of glycogenolysis

  22. Beta-Adrenergic Antagonists II: Propranolol • Pharmacologic effects • Pharmacokinetics • Therapeutic uses • Adverse effects • Bradycardia • AV heart block • Heart failure • Rebound cardiac excitation

  23. Beta-Adrenergic Antagonists II: Propranolol • Adverse effects (cont’d) • Bronchoconstriction • Inhibition of glycogenolysis • CNS effects • Precautions, warnings, and contraindications • Severe allergy • Diabetes • Cardiac, respiratory, and psychiatric disorders

  24. Beta-Adrenergic Antagonists II: Propranolol • Drug interactions • Calcium channel blockers • Insulin • Preparations, dosage, and administration • General dosing considerations • Preparations • Dosage

  25. Beta-Adrenergic Antagonists II: Metoprolol • Pharmacologic effects • Pharmacokinetics • Therapeutic uses • Adverse effects • Precautions, warnings, and contraindications • Preparations, dosage, and administration

  26. Beta-Adrenergic Antagonists II: Other Beta-Adrenergic Blockers • Receptor specificity: selective blockade • Pharmacokinetics • Therapeutic uses • Adverse effects • Intrinsic sympathomimetic activity (partial agonist activity) • Dosage and administration

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