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Chapter 45

Chapter 45. Calcium Channel Blockers. 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

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Chapter 45

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  1. Chapter 45 Calcium Channel Blockers

  2. 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

  3. 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

  4. 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

  5. Physiologic Functions and Consequences of Blockade • Heart • Myocardium • Sinoatrial (SA) node • Atrioventricular (AV) node • Coupling of cardiac calcium channels to beta1-adrenergic receptors

  6. Fig. 45–1. Coupling of cardiac calcium channels with beta1-adrenergic receptors.

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. Verapamil (Calan, Covera-HS, Isoptin, Verelan) • Adverse effects (cont’d) • Dizziness • Facial flushing • Headache • Edema of ankles and feet • Gingival hyperplasia • Heart block

  14. Verapamil (Calan, Covera-HS, Isoptin, Verelan) • Drug interactions • Digoxin • Beta-adrenergic blocking agents • Toxicity • Severe hypotension • Bradycardia and AV block • Ventricular tachydysrhythmias

  15. 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.

  16. 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

  17. Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) • Therapeutic uses • Angina pectoris • Hypertension • Cardiac dysrhythmias • Atrial flutter, atrial fibrillation, paroxysmal tachycardia

  18. 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

  19. Diltiazem (Cardizem, Dilacor-XR, Tiazac, Others) • Drug interactions • Digoxin • Beta-adrenergic blocking agents

  20. 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

  21. 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 pre-existing cardiac disorders

  22. 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

  23. Nifedipine (Adalat, Nifedical, Nifediac, Procardia) • Vasodilation by blocking calcium channels • Net effect • Lowered blood pressure • Increased heart rate • Increased contractile force

  24. Nifedipine (Adalat, Nifedical, Nifediac, Procardia) • Therapeutic uses • Angina pectoris • Hypertension • Investigational basis to relieve migraine headache and to suppress preterm labor

  25. Nifedipine (Adalat, Nifedical, Nifediac, Procardia) • Adverse effects • Flushing • Dizziness • Headache • Peripheral edema • Gingival hyperplasia • Chronic eczematous rash in older patients

  26. 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

  27. 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

  28. 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

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