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Chapter 45: Calcium Channel Blockers

Calcium Channel BlockersChapter 45
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