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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 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 Therapeutic Applications of Alpha Blockade * Essential hypertension • Lower 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 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 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 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 Reduces 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 Adverse Effects of Alpha1 Blockade * Reflex tachycardia • Reflex to increase heart rate via the ANS * Nasal congestion • Dilate the blood vessels of the nasal mucosa * Inhibition of ejaculation • • Alpha1 activation required for ejaculation Impotence is reversible; resolves when drug discontinued * Sodium retention and increased blood volume • • Reduced BP promotes renal retention of sodium and water Usually combined with diuretic when used for hypertension Adverse Effects of Alpha2 Blockade * The most significant adverse effect associated with alpha2 blockade – potentiation of the reflex tachycardia Alpha-Adrenergic Antagonists II Prazosin Terazosin Doxazosin Tamsulosin Alfuzosin Phentolamine Phenoxybenzamine Prazosin * * * * Actions and uses Pharmacokinetics Adverse effects Preparations, dosage, and administration Terazosin * * * * Actions and uses Pharmacokinetics Adverse effects Preparations, dosage, and administration Doxazosin * * * * Actions and uses Pharmacokinetics Adverse effects Preparations, dosage, and administration Tamsulosin * * * * * Actions and uses Pharmacokinetics Adverse effects Drug interactions Preparations, dosage, and administration Alfuzosin * * * * * Actions and uses Pharmacokinetics Adverse effects Drug interactions Preparations, dosage, and administration Phentolamine * Actions and uses * Adverse effects * Preparations, dosage, and administration Phenoxybenzamine * Actions and uses * Adverse effects * Preparations, dosage, and administration Beta-Adrenergic Antagonists I Therapeutic applications of beta blockade • • • • • • • • • Angina pectoris Hypertension cardiac dysrhythmias Myocardial infarction Heart failure Hyperthyroidism Migraine Stage fright Pheochromocytoma Glaucoma Beta-Adrenergic Antagonists I * Adverse effects of beta blockade • Adverse effects involve both beta1 and beta2 blockade Beta-Adrenergic Antagonists I Adverse effects of beta1 blockade Bradycardia Reduced cardiac output Precipitation of heart failure AV heart block Rebound cardiac excitation Beta-Adrenergic Antagonists I * Adverse effects of beta2 blockade Bronchoconstriction Inhibition of glycogenolysis Beta-Adrenergic Antagonists II: Propranolol * * * * Pharmacologic effects Pharmacokinetics Therapeutic uses Adverse effects Bradycardia AV heart block Heart failure Rebound cardiac excitation Beta-Adrenergic Antagonists II: Propranolol * Adverse effects (cont’d) • Bronchoconstriction • Inhibition of glycogenolysis • CNS effects * Precautions, warnings, & contraindications • Severe allergy • Diabetes • Cardiac, respiratory, and psychiatric disorders Beta-Adrenergic Antagonists II: Propranolol * Drug interactions • Calcium channel blockers • Insulin * Preparations, dosage, and administration • General dosing considerations • Preparations • Dosage Beta-Adrenergic Antagonists II: Metoprolol * * * * * * Pharmacologic effects Pharmacokinetics Therapeutic uses Adverse effects Precautions, warnings, and contraindications Preparations, dosage, and administration Beta-Adrenergic Antagonists II: Other Beta-Adrenergic Blockers Receptor specificity Pharmacokinetics Therapeutic uses Adverse effects Intrinsic sympathomimetic activity (partial agonist activity) * Dosage and administration * * * * * Questions
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