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Antiarrhythmics
Block II Pharmacology
43
Pharmacology
Graduate
10/18/2010

Additional Pharmacology Flashcards

 


 

Cards

Term
Types of Antiarrhythmic Agents
Definition

Sodium channel blockers

Sympathetic cascade blockers

Potassium channel blockers

Calcium channel blockers

Term
How antiarrhythmic drugs work
Definition

Selectively target ectopic pacemakers and decrease their automaticity (more than the SA node)

Reduce conduction/excitability

Increase refractory period

 

Steady state reduction in the number of available unblocked channels

Prolongation of the recovery time of sodium channels

Term
Class I antiarrhythmics
Definition

Sodium channel blockade

3 subclasses

Term

Class IA antiarrhythmics

Mechanism of Action

Definition

Prolong the action potential duration by slowing upstroke

Prolong QT interval by blockade of K channels

Increased QRS duration by slowing conduction in conduction system


Dissociate from channel with intermediate kinetics



Examples = procainamide, quinidine, disopyramide

Term

Class IA antiarrhythmics

Extracardiac Effects

Definition

Peripheral vascular resistance

Hypotension

Term

Class IA antiarrhythmics

Toxicity

Definition

Action potential prolongation
QT prolongation

Induction of torsade de pointes

Arrythmia

Syncope

 

Excessive slowing of conduction sys -> new arrhythmias

Term
Procainamide
Definition

Class IA antiarrythmic

Can cause SLE like symptoms in 1/3 of patients

 

Eliminated by hepatic metabolism to NAPA (t1/2: 3-4 hrs)

NAPA eliminated by kidney (can cause torsade)

Term
Disopyramide
Definition

Class IA antiarrhythmic

Can cause anti-muscarinic effects (dry)

More pronounced effects

 

Need to be given with a drug that slows AV conduction when used for atrial fibrillation

Half life = 7-8 hours

Term
Quinidine
Definition

Type IA antiarrythmic

Some antimuscarinic effects (dry)

 

Half life = 6-8 hours

Term
Therapeutic use for procainamide
Definition

Effective against atrial and ventricular arrhythmias

Requires frequent dosing, not good for long term

 

Term

Therapeutic use for quinidine

 

Definition

Rarely used

Maintain normal sinus rhythm in patients with normal hearts but with atrial flutter or fibrillation

Patients treated with quinidine more likely to have normal sinus rhythm, but 2-3x increase in death

 

Term

Therapeutic use for disopyramide

 

Definition

Rarely used

Only approved for treatment of ventricular arrhythmias in the US

Term

Class IB Antiarrythmics

Mechanism of action

Definition

Shorten the action potential duration

Dissociate from channel with rapid kinetics

Preferentially affect more depolarized tissues

No effect on conduction

Increased inactivation and slow unbinding kinetics -> selective depression of conduction in depolarized cells, little effect on normal cardiac cells

Examples: lidocaine, mexiletine

Term

Lidocaine

Cardiac Toxicity

Definition

Lowest cardiotoxicity of all sodium  blockers

Proarrhythmic effects: SA node arrest, worsening of impaired conduction, ventricular arrhythmia

In large doses, may decrease contractility, causing hypotension in patients with preexisting heart failure

 

 

Term

Lidocaine

Extracardiac toxicity

Definition

Dose related

Local anesthetic .: neurologic effects

Paresthesia, tremor, nausea of central origin, lightheadedness, hearing disturbances, slurred speech, and convulsions.

Term

Lidocaine

Pharmacokinetics

Definition

Extensive first pass hepatic metabolism

Only 3% of orally administered drug makes it to plasma

 

Usually given parenterally

T 1/2: 1-2 hours

Term

Lidocaine

Therapeutic Uses

Definition

Highly effective for arrhythmias from acute MI (metabolic injury)

Agent of choice for termination of ventricular tachycardia and prevention of ventricular fibrillation after cardioversion during acute ischemia

Term
Mexiletine
Definition

Class IB Antiarrhythmic

Orally active cogener of lidocaine

Similar function

T 1/2: 8-20 hours

 

Used for chronic pain due to diabetic neuropathy and/or nerve injury

Term
Class IC Antiarrhythmics
Definition

Minimal effects of action potenial duration

Dissociate from channel with slow kinetics

 

Used for patients with otherwise normal hearts with supraventricular rhythms

 

Examples: flecainide, moricizine, propafenone

Term

Class IC Antiarrhythmics

Toxicity

Definition

Provocation or exacerbation of arrhythmia

Can accelerate ventricular rate in patients with atrial flutter

Can increase frequency of episodes of re-entrant ventricular tachycardia

Term

Flecainide

Pharmacokinetics

Definition

Elimination by renal excretion of unchanged drug AND

hepatic metabolism to inactive metabolites

 

T 1/2 = 10-17 hours (depends on urinary pH)

 

Term
Morcizine
Definition

Type IC Antiarrhythmic

Many metabolites, some which can remain active and have long half-lives

Term
Class II Antiarrhythmics
Definition

Beta-adrenoceptor blocking drugs, examples: propanolol, esmolol


Reduce cAMP -> reduction in sodium, calcium current -> suppression of abnormal pacemakers

AV node particularly sensitive, prolong the PR interval

 

Safer than class I, used to control ventricular contraction in a-fib/flutter

Contraindicated for patients with Wolff-Parkinson-White

Term
Propanolol
Definition

Class II Antiarrhythmic

Non-selective beta adrenoceptor antagonist

 

T 1/2 = 3-6 hours

Term
Esmolol
Definition

Type II antiarrhythmic

IV cardioselective/beta-1 selective agent


T 1/2 = 9 minutes

Effects disappear within 30 mins after stopping the infusion

Effective in controlling the ventricular response to atrial flutter/fibrillation, especially after cardiac surgery

 

Term

Esmolol

Adverse Effects

Definition

Hypotension

Bradycardia

Usually stop within 30 minutes after infusion terminated

Term
Class III Antiarrhythmics
Definition

Prolong effective refractory period by prolonging action potential, examples: sotalol, ibutilide

 

Blockade of Ik potassium channels OR enhance inward current

Reduces ability for heart to respond to tachycardia

Increase QT interval

 

Term
Class III Antiarrhythmic Side Effects
Definition

Reverse use dependent: most reduction at lower heart rates

Can induce torsade de pointes at lower heart rates

Term
Sotalol
Definition

Class III antiarrhythmic, nonselective beta-blocking drug

More effective for arrhythmias than beta blockers because of Ik inhibition

T1/2 = 12 hours

Approved for treatment of life-threatening ventricular arrhythmias and maintenance of sinus rhythm in patients with atrial fibrillation

Approved for supraventricular and ventricular arrhythmias in pediatric population

Term

Sotalol

Adverse effects

Definition

Dose related torsade de pointes

Excessive beta blockade -> sinus bradycardia, asthma

 

 

Term
Amiodarone
Definition

Class III Antiarrhythmic, most efficacious of all antiarrhythmics

Can block sodium, calcium, potassium channels and beta aderenoceptors


Only used for arrhythmias that are resistant to other drugs

Rapid elimination (3-10 days), slower component (weeks)

Effects for 1 to 3 months

Term

Amiodarone

Toxic effects

Definition

Many toxic effects

Microcrystalline deposits in cornea and skin

Thyroid dysfunction

Parasthesias

Tremor

Pulmonary Fibrosis

Term

Amiodarone

Therapeutic Uses

Definition

Most effective in preventing recurrences of a-fib, VT, v-fib

Increase in mortality in patients with CAD, CHF

 

Term
Ibutilide
Definition

Slows cardiac repolarization of Ik

May induce expression of slow inward Na current

 

Adverse effect: excessive QT interval, torsades de pointes

 

IV used for acute a flutter, a-fib

Term
Dofetilide
Definition

Class III Antiarrhythmic

Slows cardiac repolarization by blockade of Ikr

Torsades de pointes

 

Approved for maintenance of normal sinus rhythm in patients with a-fib

Term
Dronedarone
Definition

Class III Antiarrhythmic

Structural analog of amiodarone

 

First antiarrhythmic to demonstrate a reduction in mortality or hospitalization of patients with a-fib

Term
Vernakalant
Definition

Type III antiarrhythmic

Investigational mulit channel blocker

Developed for treatment a-fib

 

Term
Class IV Antiarrhythmics
Definition

Calcium channel blockers, prototype: verapamil, dilitazem


Extensively metabolized by liver

T 1/2: 7 hrs (V), 4 hrs (dil)


Block activated and inactivated L-type calcium channels

Increase refractory period (PR interval increased)

Cause peripheral vasoconstriction

Term
Verapamil/dilitazem toxicity
Definition

Dose related, usually avoidable

AV block with large doses or AV node disease

 

Constipation, lassitude, nervousness, peripheral edema

 

Contraindicated in Wolff-Parkinson-White syndrome

Term

Therapeutic use

Verapamil/dilitazem

 

Definition

Adults with heart failure, SA/AV nodal disease

To terminate supraventricular tachycardia (adenosine preferred)

Used in patients to prevent recurrence

Term
Adenosine
Definition

Activate inward rectifier K+ current, inhibit Ca current

Hyperpolarization and suppression of calcium dependent action potentials

Directly inhibits AV nodal conduction

Increases AV nodal refractory period (smaller effect on SA) High efficacy, short duration of action


Drug of choice for conversion of paroxysmal supraventricular tachycardia to sinus rhythm

 

Term
Magnesium
Definition

Antiarrhythmic effects even with normal Mg levels

Indicated for digitalis-induced arrhythmias

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