Calcium Channel Blockers

Question 1

§ Calcium channels open =

Answer 1

Contractile process

Question 2

Calcium channels blocked

Answer 2

Vasodilation

Question 3

Verapamil and diltiazem

Answer 3

§ 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

§ 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

Question 4

Verapamil

Answer 4

§ Therapeutic uses § Angina pectoris
§ Vasospastic angina and angina of effort § Essential hypertension
§ Second-line agent after thiazide diuretics § Cardiac dysrhythmias
§ Atrial flutter, atrial fibrillation, paroxysmal supraventricular tachycardia § Migraine

Adverse effects § Constipation
§ Most common complaint
§ Results from blockade of calcium channels in smooth muscle of the intestine § Especially severe for older adults
§ Can be decreased by increasing dietary fiber and fluids

Dizziness
§ Facial flushing § Headache
§ Edema of ankles and feet § Gingival hyperplasia
§ Heart block

§ Drug interactions § Digoxin
§ Beta-adrenergic blocking agents
§ Toxicity
§ Severe hypotension
§ Bradycardia and AV block
§ Ventricular tachydysrhythmias
§ Gastric lavage and activated charcoal

§ IV verapamil for dysrhythmias can cause severe cardiovascular effects
§ Blood pressure and ECG should be monitored
§ Resuscitation equipment should be kept immediately available

Question 5

Diltiazem (cardizem)

Answer 5

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 the heart

Therapeutic uses
§ Angina pectoris
§ Hypertension
§ Cardiac dysrhythmias
§ Atrial flutter, atrial fibrillation, paroxysmal tachycardia

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

§ Drug interactions § Digoxin
§ Beta-adrenergic blocking agents

Question 6

Nifedipine

Answer 6

§ Minimal blockade of calcium channels in the heart

Vasodilation by blocking calcium channels
§ Blocks in vascular smooth muscle
§ Very little blockade of heart calcium (Ca) channels
§ Cannot be used to treat dysrhythmias
§ Less likely than verapamil to exacerbate preexisting cardiac disorders

§ 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 immediate release versus sustained release

§ Vasodilation by blocking calcium channels § Net effect
§ Lowered blood pressure
§ Increased heart rate
§ Increased contractile force

§ Therapeutic uses
§ Angina pectoris
§ Hypertension
§ Investigational basis: To relieve migraine headache and to suppress preterm labor

§ Adverse effects § Flushing
§ Dizziness
§ Headache
§ Peripheral edema
§ Gingival hyperplasia
§ Chronic eczematous rash in older patients

§ Adverse effects
§ Reflex tachycardia
§ Increases cardiac oxygen demand
§ Can increase pain in angina 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

§ Immediate release (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 that these be used with great caution

Question 7

Dihydropyridines

Answer 7

§ Produce greater blockade of Ca channels in the VSM than in the heart
§ Nicardipine, amlodipine, isradipine, felodipine, nimodipine, nisoldipine, and clevidipine