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Chapter 45: Calcium Channel Blockers
Calcium Channel Blockers | Chapter 45 |
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Three Classifications of CCB's | 1. Dihydropyridines 2. Phenylalkylamine 3. Benzothizepine Also known as calcium antagonists and slow channel blockers |
Dihydropyridines | Nifedipine [Adalat, Procardia] Dihydropyridines: Agents that act mainly on vascular smooth muscle |
Phenylalkylamine | Verapamil [Calan, Isoptin] Acts on vascular smooth muscle and the heart |
Benzothazepine | Diltiazem [Cardiazem,Tiazac, others] Acts on vascular smooth muscle and the heart |
CCB | Blocks calcium access to the cells causing a decrease in contractility, ateriolar constriction, PVR (peripheral vascular resistance), and BP Widely used to treat hypertension, angina pectoris, and cardiac dysrhythmias. |
Calcium role in body | Plays a critical role in the function of vascular smooth muscle (VSM) and the heart. Hypercalcemia: Cardiac dysrythmias (decreased QT interval and shortened ST segments; Decreased CNS. Anorexia, nausea; constipation; Decreased LOC; Calcium level > 10.5 |
Verapamil: Classification/Name/Mode of Action | Classification: Phenylalkyamine Name: Verapamil [Calan] Act on arterioles and on the heart (reduces AV conduction) Safe Dose Range: Oral: IR (40,80,120 mg) SR (120, 180, 240 mg); IV |
Verapamil: Therapeutic uses | Angina pectoris: used for angina pectoris; vasodilates Essential HTN: used for chronic HTN Lowers BP by dilating arterioles Cardiac Dysrhythmias: slows ventricular rate for A. flutter, A. Fib, paroxysmal supraventricular tachycardia |
Verapamil: Essential HTN: Mode of Action | Essential HTN: Verapamil is a second-line agent for chronic HTN, used after thaizide diuretics. Lowers BP by dilating arterioles |
Verapamil: Cardiac dysrthymias: Mode of Action | Cardiac dysrhythmias: (IV) used to slow ventricular rate in patients with atrial flutter, atrial fibrillation, and paroxysmal supraventrivular tachycardia. Benefits: supress impulse conduction through AV node to prevent atria from driving the ventricles |
Drug-Drug Interactions: Verapamil + Digoxin | Both suppress impulse conduction through the AV node. Risk of AV block and digoxin toxicity when used concurrently. Verapamil increases plasma levels of digoxin by about 60%. |
Drug-Drug Interactions: Verapamil + Beta-Adrenergic Blocking Agents | Risk of excessive cardiosuppression because they both decrease HR, AV conduction, and contractility. To avoid this as much as possible both drugs should be given several hours apart. |
Drug-Drug Interactions: Verapamil + Grapefruit Juice | GJ can inhibit the intestinal and hepatic metabolism and thus raises the plasma levels approx. 8 to 24 times higher. |
Verapamil: Toxicity 1/3 | S/S of Toxicity: severe hypotension and cardiotoxicity (bradycardia, AV block, Ventricular tachydysrhythmias) Tx: PO: Gastric lavage, activate charcoal. IV: Calcium gluconate to reverse vasodialtion and negative inotropic effects except AV block |
Verapamil: Toxicity 2/3 | Hypotension treatment: IV norepinephrine promoting vasoconstriction, increases CO, and Trendelburg's position. |
Verapamil: Toxicity 3/3 | Bradycardia and AV block: Atropine (blocks parasympathetic influences), electronic pacing, and glucagon (increases amounts of intracellular cAMP). Ventricular Tachydysrhythmias: Direct cardioversion (DC), procainamide/ lidocaine. |
Verapamil: SE/RN considerations: Common effects | Common effects: constipation (increase dietary fiber and fluids). Results from blockade of Ca2+ channels in smooth muscles of intestines. Other: dizziness, facial flushing, HA, and edema of ankles and feet. |
Verapamil: SE/RN considerations Cardiac effects | Cardiac effects: SA node= bradycardia; AV node= partial or complete AV block; Myocardium= blockade can decrease contractility. Exacerbates cardiac dysfunction of a sick heart. DO NOT USE W/PT's THAT HAVE SICK SINUS SYNDROME or 2nd/3rd DEGREE AV BLOCK. |
Verapamil Patient Education | Increase dietary fiber, fluid intake, and exercise. Avoid overexertion when anginal pain is relieved. Take with meals or milk. Do not chew or crush SR. Avoid grapefruit juice. |
RN interventions: | Monitor hepatic and renal function studies. Monitor ECG and avoid giving when heart blocks are present. |
Amlodipine:Interventions/Drug-Drug interactions/S/S of toxicity can be found under verapamil | Classification: Dihydropyridines Prototype: Norvasac Like nifedipine, Amlodipine produces greater blockade of Ca++ channels in VSM than in the heart. |
Amlodipine [Norvasac]: Dosage/ Mode of action | Safe Dose Range: Given PO and absorbed slowly. Initial dosage for HTN and angina is 5 mg q 24-hrs. Mode of Action: Calcium channel blockade of vessels and minimal blockade of heart; promotes vasodilation; causes little reflex tachycardia. |
Amlodipine [Norvasac]: Adverse Efftects | Adverse Effects: Peripheral and facial edema, flushing, dizziness, HA, as may eczematous rash in older patients. |
Five direct hemodynamic effects of Verapamil and Diltiazem: | 1. Blockade at peripheral arterioles - Reduces arterial pressure 2. Blockade at arteries and arterioles of heart - Increases coronary perfusion 3. Blockade at SA node - Reduces HR 4. Blockade at AV node (most important) - Decreases AV condu |
Physiologic Function of CCB's | Calcium channels open = Contractile process Calcium channels blocked = Vasoconstriction |