Antidysrhythmic Drugs Flashcards
Quinidine
Sodium Channel Blockers class IA agents
Ø Effects on the heart • Blocks sodium channels • Slows impulse conduction • Delays repolarization • Blocks vagal input to the heart Ø Effects on the ECG • Widens the QRS complex • Prolongs the QT interval Ø Therapeutic uses • Used for supraventricular and ventricular dysrhythmias
Ø Adverse effects • Diarrhea • Cinchonism • Cardiotoxicity • Arterial embolism • Alpha-adrenergic blockade, resulting in hypotension • Hypersensitivity reactions Ø Drug interactions • Digoxin
Procainamide [Procanbid]
Sodium Channel Blockers class IA agents
Ø Similar to quinidine
Ø Only weakly anticholinergic
Ø Adverse effects: Symptoms of systemic lupus erythematosus
Disopyramide [Norpace]
Ø Similar to quinidine
Ø Prominent side effects have limited its use
Lidocaine [Xylocaine]
Class IB Agents
• Blocks cardiac sodium channels Slows conduction in the atria, ventricles, and His-Purkinje system • Reduces automaticity in the ventricles and His-Purkinje system • Accelerates repolarization Ø Adverse effects • CNSeffects • Drowsiness • Confusion • Paresthesias
Ø Phenytoin
Antiseizure medication also used to treat digoxin-induced
dysrhythmias
Mexiletine
- Oral analog of lidocaine
* Used for symptomatic ventricular dysrhythmias
Ø Flecainide
Ø Propafenone
Class IC Agents
Block cardiac sodium channels Delay ventricular repolarization All class IC agents can exacerbate existing dysrhythmias and create new ones
Propranolol [Inderal]:
Nonselective beta- adrenergic antagonist
Ø Effects on the heart and ECG
• Decreased automaticity of the SA node
• Decreased velocity of conduction through the AV node • Decreased myocardial contractility
Ø Therapeutic use
• Dysrhythmias caused by excessive sympathetic stimulation
• Supraventricular tachydysrhythmias Suppression of excessive discharge Slowing of ventricular rate
Ø Adverse effects • Heart block • Heart failure • AV block • Sinus arrest • Hypotension • Bronchospasm (in asthma patients) Other class II: Beta blockers Ø Acebutolol [Sectral] Ø Esmolol [Brevibloc]
Amiodarone [Cordarone, Pacerone]
Potassium Channel Blockers
Ø Therapeutic use
• For life-threatening ventricular dysrhythmias only
• Recurrent ventricular fibrillation
• Recurrent hemodynamically unstable ventricular tachycardia
Ø Effects on the heart and ECG • Reduced automaticity in the SA node • Reduced contractility • Reduced conduction velocity • QRS widening • Prolongation of the PR and QT intervals
Adverse effects • Protracted half-life • Pulmonary toxicity • Cardiotoxicity • Toxicity in pregnancy and breastfeeding • Corneal microdeposits • Optic neuropathy
Drug interactions (increases levels) • Quinidine • Diltiazem • Cyclosporine • Digoxin • Procainamide • Diltiazem • Phenytoin • Warfarin • Lovastatin, simvastatin, atorvastatin
Amiodarone levels can be increased by grapefruit juice and by inhibitors of CYP3A4. Toxicity can result.
Amiodarone levels can be reduced by cholestyramine (which decreases amiodarone absorption) and by agents that induce CYP3A4 (e.g., St. John’s wort, rifampin).
Dronedarone [Multaq]
Derivative of amiodarone
Ø Effects on the heart and ECG Ø Pharmacokinetics
Ø Adverse effects
• Common side effects
• Cardiac effects in severe heart failure
• Liver toxicity
• Toxicity in pregnancy and breastfeeding
Ø Drug interactions
• Multiple; many involve CYP3A4
Potassium Channel Blockers
Sotalol [Betapace]
Ø Combined class II and class III properties Ø Beta blocker that also delays repolarization
Dofetilide [Tikosyn]
Ø Oral class III antidysrhythmic
Ø Predisposes patient to torsades de pointes
Ibutilide [Covert] Ø Class III agent
Ø IV agent used to terminate atrial flutter/fibrillation
Verapamil [Calan, Covera, Verelan] and diltiazem [Cardizem]
Calcium Channel Blockers
Ø Reduce SA nodal automaticity Ø Delay AV nodal conduction
Ø Reduce myocardial contractility
Ø Therapeutic uses
• Slow ventricular rate (atrial fibrillation or atrial flutter)
• Terminate SVT caused by an AV nodal reentrant circuit
Ø Adverse effects • Bradycardia • Hypotension • AV block • Heart failure • Peripheral edema • Constipation • Can elevate digoxin levels • Increased risk when combined with a beta blocker
Adenosine [Adenocard]
Ø Effects on the heart and ECG
• Decreases automaticity in the SA node • Slows conduction through the AV node • Prolongs PR interval
Ø Therapeutic use: Termination of paroxysmal SVT
Ø Adverse effects • Sinus bradycardia • Dyspnea • Hypotension • Facial flushing • Chest discomfort Ø Drug interactions • Methylxanthines • Dipyridamole
Digoxin [Lanoxin]
Ø Primary indication is heart failure
Ø Also used to treat supraventricular dysrhythmias (inactive against ventricular dysrhythmias)
• Suppresses dysrhythmias by decreasing conduction through AV node and automaticity in the SA node
• QT interval may be shortened
Ø Adverse effect: Cardiotoxicity • Risk increased by hypokalemia
