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Chapter 45 Calcium Channel Blockers Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. Calcium Channel Blockers Drugs that prevent calcium ions from entering cells Greatest impact on heart and blood vessels Used to treat hypertension, angina pectoris, and cardiac dysrhythmias Controversy: safety for patients with hypertension and diabetes Also known as calcium antagonists and slow channel blockers Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 2 Calcium Channel Blockers Calcium channels: physiologic functions and consequences of blockade Calcium channel blockers: classification and sites of action Verapamil and diltiazem: agents that act on vascular smooth muscle and the heart Dihydropyridines: agents that act mainly on vascular smooth muscle Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 3 Physiologic Functions and Consequences of Blockade Vascular smooth muscle Calcium channels open = Contractile process Calcium channels blocked = Vasoconstriction Therapeutic doses Selectively on peripheral arterioles and arteries and arterioles of the heart No significant effect on veins Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 4 Physiologic Functions and Consequences of Blockade Heart Myocardium Sinoatrial (SA) node Atrioventricular (AV) node Coupling of cardiac calcium channels to beta1adrenergic receptors Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 5 Fig. 45–1. Coupling of cardiac calcium channels with beta1-adrenergic receptors. Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 6 Classification and Sites of Action Classification Dihydropyridines—nifedipine Phenylalanine—verapamil Benzothiazepine—diltiazem Sites of action Dihydropyridines act primarily on arterioles Verapamil and diltiazem act on arterioles and on the heart Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 7 Verapamil and Diltiazem Agents that act on vascular smooth muscle and the heart Hemodynamic effects Direct effects on the heart and blood vessels Indirect (reflex) effects Net effects Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 8 Verapamil and Diltiazem: Hemodynamic Effects Five direct hemodynamic effects Blockade at peripheral arterioles • Reduces arterial pressure Blockade at arteries and arterioles of heart • Increases coronary perfusion Blockade at SA node • Reduces heart rate Blockade at AV node (most important) • Decreases AV nodal conduction Blockade in the myocardium • Decreases force of contraction Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 9 Verapamil and Diltiazem: Hemodynamic Effects Indirect (reflex) hemodynamic effects Baroreceptor reflex Net effects Little or no net effect on cardiac performance Vasodilation accompanied by reduced arterial pressure and increased coronary perfusion Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 10 Verapamil (Calan, Covera-HS, Isoptin, Verelan) Therapeutic uses Angina pectoris • Vasospastic angina and angina of effort Essential hypertension • First-line agent Cardiac dysrhythmias • Atrial flutter, atrial fibrillation, paroxysmal supraventricular tachycardia Migraine Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 11 Verapamil (Calan, Covera-HS, Isoptin, Verelan) Adverse effects Constipation • Most common complaint • Results from blockade of calcium channels in smooth muscle of the intestine • Especially severe for the elderly • Can be decreased by increasing dietary fiber and fluids Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 12 Verapamil (Calan, Covera-HS, Isoptin, Verelan) Adverse effects (cont’d) Dizziness Facial flushing Headache Edema of ankles and feet Gingival hyperplasia Heart block Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 13 Verapamil (Calan, Covera-HS, Isoptin, Verelan) Drug interactions Digoxin Beta-adrenergic blocking agents Toxicity Severe hypotension Bradycardia and AV block Ventricular tachydysrhythmias Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 14 Verapamil (Calan, Covera-HS, Isoptin, Verelan) IV verapamil for dysrhythmias can cause severe cardiovascular effects. Blood pressure and ECG should be monitored with resuscitation equipment immediately available. Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 15 Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) Actions and uses Blocks calcium channels in the heart and blood vessels (similar to verapamil) Lowers blood pressure • Arteriolar dilation • Direct suppressant/reflex cardiac stimulation = Little net effect on heart Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 16 Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) Therapeutic uses Angina pectoris Hypertension Cardiac dysrhythmias • Atrial flutter, atrial fibrillation, paroxysmal tachycardia Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 17 Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) Adverse effects Similar to verapamil, except for less constipation Dizziness Flushing Headache Edema of ankles and feet Exacerbates bradycardia, sick sinus syndrome, heart failure, second- or third-degree heart block Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 18 Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) Drug interactions Digoxin Beta-adrenergic blocking agents Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 19 Dihydropyridines Agents that act mainly on vascular smooth muscle Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Significant blockade of calcium channels in blood vessels Minimal blockade of calcium channels in the heart Similar to verapamil in some respects and quite different in others Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 20 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Vasodilation by blocking calcium channels Blocks in vascular smooth muscle Very little blockade of heart Ca channels Cannot be used to treat dysrhythmias Less likely than verapamil to exacerbate preexisting cardiac disorders Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 21 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Direct effects Limited to blockade of Ca channels in vascular smooth muscle (VSM) • No direct suppressant effects on: Automaticity, AV conduction, or contractile force Indirect effects Lowered blood pressure (BP) activates baroreceptor reflex Primarily with fast-acting vs. sustained-release Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 22 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Vasodilation by blocking calcium channels Net effect • Lowered blood pressure • Increased heart rate • Increased contractile force Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 23 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Therapeutic uses Angina pectoris Hypertension Investigational basis to relieve migraine headache and to suppress preterm labor Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 24 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Adverse effects Flushing Dizziness Headache Peripheral edema Gingival hyperplasia Chronic eczematous rash in older patients Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 25 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Adverse effects (cont’d) Reflex tachycardia Increases cardiac oxygen demand Can increase pain for anginal patients Can be combined with a beta blocker for prevention of reflex tachycardia • Note: Beta blockers decrease the adverse cardiac effects of nifedipine, but can intensify the adverse cardiac effects of verapamil and diltiazem Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 26 Nifedipine (Adalat, Nifedical, Nifediac, Procardia) Adverse effects (cont’d) Rapid-acting nifedipine (not sustained) • Has been associated with increased mortality in patients with MI and unstable angina • Other rapid-acting calcium channel blockers also associated • No cause-and-effect relationship established • National Heart, Lung, and Blood Institute (NHLBI) recommends these be used with great caution Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 27 Dihydropyridines Seven other dihydropyridines available All similar to nifedipine Produce greater blockade of Ca channels in the VSM than in the heart Nicardipine, amlodipine, isradipine, felodipine, nimodipine, nisoldipine, and clevidipine Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc. 28
