Chapter 45: Calcium Channel Blockers
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| Three Classifications of CCB's | 1. Dihydropyridines
2. Phenylalkylamine
3. Benzothizepine
Also known as calcium antagonists and slow channel blockers
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| Dihydropyridines | Nifedipine [Adalat, Procardia]
Dihydropyridines: Agents that act mainly on vascular smooth muscle
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| Phenylalkylamine | Verapamil [Calan, Isoptin]
Acts on vascular smooth muscle and the heart
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| Benzothazepine | Diltiazem [Cardiazem,Tiazac, others]
Acts on vascular smooth muscle and the heart
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| 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.
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| 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
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| 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
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| 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
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| 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
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| 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
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| 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%.
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| 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.
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| 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.
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| 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
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| Verapamil: Toxicity 2/3 | Hypotension treatment: IV norepinephrine promoting vasoconstriction, increases CO, and Trendelburg's position.
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| 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.
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| 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.
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| 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.
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| 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.
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| RN interventions: | Monitor hepatic and renal function studies. Monitor ECG and avoid giving when heart blocks are present.
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| 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.
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| 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.
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| Amlodipine [Norvasac]: Adverse Efftects | Adverse Effects: Peripheral and facial edema, flushing, dizziness, HA, as may eczematous rash in older patients.
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| 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
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| Physiologic Function of CCB's | Calcium channels open = Contractile process
Calcium channels blocked = Vasoconstriction
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