Anti-arrhythmia drugs

Question 1

Classification of arrhythmic drugs

Answer 1

Class 1A, 1B, 1C, II, III & IV

Question 2

Example of Class 1A drug (Na+ channel blockers)

Answer 2

Procainamide

Question 3

MOA of Class 1A drug (Na+ channel blockers)

Answer 3

1. reduces rate of phase 0 rise (slows phase 0 depolarisation)
2. reduce conductivity and automaticity
3. increase ERP and APD

Question 4

Example of Class 1B drug (Na+ channel blockers)

Answer 4

Lidocaine

Question 5

MOA of Class 1B drug (Na+ channel blockers)

Answer 5

1. reduces rate of phase 0 rise
2. shortens phase 3 repolarisation
3. reduces automaticity (little effect on conductivity)
4. reduces APD
5. no change in ERP

Question 6

Example of Class 1C drug (Na+ channel blockers)

Answer 6

Flecainide

Question 7

MOA of class 1C drug (Na+ channel blockers)

Answer 7

1. reduces rate of phase 0 rise
2. shortens phase 3 repolarisation
3. reduces conductivity and automaticity
4. no/little effect on APD/ERP

Question 8

Clinical uses for class 1C drug (Na+ channel blockers)

Answer 8

Refractory ventricular tachycardias that tend to progress to VF

Question 9

Examples of Class II drugs (beta-blockers)

Answer 9

1. Metoprolol

2. Propranolol

Question 10

MOA of Class II drugs (beta-blockers)

Answer 10

1. reduce phase 4 depolarisation
2. reduces automaticity
3. prolonged AV conduction
4. Reduces HR and contractility
5. No change to APD, ERP

Question 11

Clinical uses of Class II drugs (beta-blockers)

Answer 11

1. Tachycardia caused by sympathetic activation
2. Atrial fibrillation
3. AV nodal reentrant tachycardia
4. Reduces sudden arrhythmic death post-MI

Question 12

Examples of Class III drug (potassium channel blockers)

Answer 12

Amiodarone

Question 13

MOA of Class III drug (potassium channel blockers)

Answer 13

1. Prolongs Phase 3 repolarisation (no phase 0 effect)

2. Increase ERP and APD

Question 14

Action of amiodarone

Answer 14

1. Blockade of Ikr and Iks (III) (main)
2. Blockade of sodium channels (I)
3. Blockade of adrenergic receptor (II)
4. Blockade of calcium channels (IV)

Question 15

PK of amiodarone

Answer 15

1. bioavailability: 35-65%
2. hepatic metabolism: desethylamiodarone (bioactive)
3. elimination h1/2: 3-10 days (first 50%), several weeks (next 50%)
4. After discontinuation: effects are maintained for 1-3 months

Question 16

Clinical uses of amiodarone

Answer 16

1. Be effective in maintaining normal sinus rhythm in patients with atrial fibrillation
2. Be effective in the prevention of reentrant ventricular tachycardia

Question 17

Adverse effect of amiodarone

Answer 17

Symptomatic bradycardia and heart block

Question 18

Examples of Class 4 Drugs (Non-DHP CCB)

Answer 18

1. Verapamil

2. Diltiazem

Question 19

MOA of Class 4 Drugs (Non-DHP CCB)

Answer 19

1. Prolongs Phase 4 depolarisation
2. Reduces conductivity on AV node
3. Increase ERP and APD

Question 20

Clinical uses of Verapamil

Answer 20

1. Supraventricular tachycardia
2. Hypertension
3. Angina

Question 21

Adverse effects of verapamil

Answer 21

1. contraindication: patients with preexisting depressed cardiac function
2. hypotension