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Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Chapter 19 Indirect-Acting Antiadrenergic Agents
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2Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Indirect-Acting Antiadrenergic Agents Prevent stimulation of peripheral adrenergic receptors Two groups Adrenergic neuron-blocking agents Decrease norepinephrine release Decrease norepinephrine release Centrally acting alpha 2 agonists Reduce impulses along the sympathetic nerves Reduce impulses along the sympathetic nerves
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3Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Centrally Acting Alpha 2 Agonists Reduce the firing of sympathetic neurons Used primarily for hypertension Effects similar to those of the direct-acting adrenergic receptor blockers
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4Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Centrally Acting Alpha 2 Agonists Clonidine Guanabenz and guanfacine Methyldopa and methyldopate
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5Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Clonidine Mechanism of antihypertensive action Selective activation of alpha 2 receptors in the CNS Reduces sympathetic outflow to blood vessels and the heart Pharmacologic effects Bradycardia and a decrease in cardiac output Minimal orthostatic hypotension
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6Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Clonidine Pharmacokinetics Lipid-soluble Readily absorbed following oral administration Therapeutic uses Two approved applications Hypertension Hypertension Severe pain Severe pain
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7Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Clonidine Adverse effects Drowsiness: 35% of patients Xerostomia: 40% of patients Rebound hypertension Withdraw slowly over 2 to 4 days Withdraw slowly over 2 to 4 days Use in pregnancy Not recommended Not recommended Other adverse effects Constipation, impotence, gynecomastia, and adverse CNS effects Constipation, impotence, gynecomastia, and adverse CNS effects Risk for abuse Risk for abuse
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8Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Clonidine Preparations, dosage, and administration Preparations Oral and transdermal Oral and transdermal Dosage and administration Transdermal applied every 7 days Transdermal applied every 7 days Applied to hairless upper arm or torso Applied to hairless upper arm or torso
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9Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Guanabenz and Guanfacine Pharmacology Very similar to that of clonidine Adverse effects Xerostomia, sedation, rebound hypertension if not weaned Dosage and administration
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10Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Methyldopa and Methyldopate Mechanism of action Lowers blood pressure (BP) by acting at sites within the CNS Causes alpha 2 activation Not an alpha 2 agonist: taken up into brainstem and converted into alpha 2 agonist Pharmacologic effects Vasodilation, not cardiosuppression Lowers BP in supine and standing subjects
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11Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Methyldopa and Methyldopate Therapeutic use Hypertension One of the earliest drugs; no longer a first-line drug Adverse effects Positive Coombs’ test and hemolytic anemia Hepatotoxicity Hepatitis, jaundice, and rarely fatal hepatic necrosis Hepatitis, jaundice, and rarely fatal hepatic necrosis Other adverse effects Xerostomia, sexual dysfunction, orthostatic hypotension, and CNS effects Xerostomia, sexual dysfunction, orthostatic hypotension, and CNS effects
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12Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Adrenergic Neuron-Blocking Agents Act presynaptically to reduce the release of norepinephrine from sympathetic neurons Very little effect on release of epinephrine from adrenal medulla Reserpine
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13Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Reserpine Mechanism of action Depletion of NE from postganglionic sympathetic neurons Closely resembles alpha and beta blockade Can cause depletion of transmitters (serotonin, catecholamines) Pharmacologic effects Peripheral effects Slows heart rate and reduces cardiac output Slows heart rate and reduces cardiac output CNS effects Sedation and state of indifference Sedation and state of indifference
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14Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Reserpine Therapeutic uses Principal indication: hypertension (but not a preferred drug) Psychotic states (but not a preferred drug) Adverse effects Depression Bradycardia, orthostatic hypotension, nasal congestion GI involvement Preparations, dosage, and administration
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15Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Fig. 19-1. Mechanism of reserpine action.
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