Na Channel Blockers (Anti-Arrhythmias)

Question 1

Quinidine

Answer 1

MOA:
– Moderate binding to Na channels –> ↑QRS interval
– Also block K channels –> ↑action potential duration (APD)
– Also block ACh –> anti-cholinergic effects

Uses:
– “Old-school” drugs, rarely used any
more due to toxicity
– Formerly used for AF & AFL,
PSVT, VT (almost everything)

Availability:
- PO or IV

Toxicity/Pearls:
-Rarely used due to multiple toxicities
* Most unique = cinchonism (headache, dizziness, tinnitus)
* Most common = GI (N/V/D)
* Most severe = thrombocytopenia, hepatitis, autoimmune reactions

Question 2

Procainamide

Answer 2

MOA:
– Moderate binding to Na channels –> ↑QRS interval
– Also block K channels –> ↑action potential duration (APD)
– Also block ACh –> anti-cholinergic effects

Uses:
– “Old-school” drugs, rarely used any
more due to toxicity
– Formerly used for AF & AFL,
PSVT, VT (almost everything)

Availability:
- IV

Toxicity/Pearls:
* Autoimmune reactions
* N-acetyl procainamide (NAPA) = active metabolite, K blocker, levels can be monitored

Question 3

Disopyramide

Answer 3

MOA:
– Moderate binding to Na channels –> ↑QRS interval
– Also block K channels –> ↑action potential duration (APD)
– Also block ACh –> anti-cholinergic effects

Uses:
– “Old-school” drugs, rarely used any
more due to toxicity
– Formerly used for AF & AFL,
PSVT, VT (almost everything)

Availability:
- PO

Toxicity/Pearls:
Highly Anticholinergic

Question 4

Lidocaine

Answer 4

MOA:
– Weak binding to Na channels –> ↔ QRS interval
– ↓action potential duration (APD)

Uses:
– Ventricular arrhythmias only

Availability:
- IV

Toxicity/Pearls:
* Short half-life –> IV bolus followed by infusion
* Levels can be monitored
* Neurologic AE’s (dizziness, tremor, confusion)

Question 5

Mexiletine

Answer 5

MOA:
– Weak binding to Na channels –> ↔ QRS interval
– ↓action potential duration (APD)

Uses:
– Ventricular arrhythmias only

Availability:
- PO

Toxicity/Pearls:
* Orally absorbable form of lidocaine, similar effects
* Gastric AE’s (nausea, heartburn)

Question 6

Flecainide

Answer 6

MOA:
– Strong binding to Na channels –> ↑↑↑ QRS interval
– ↔ action potential duration (APD)
– May also ↑PR interval, ↓contractility

Uses:
– Ventricular & supraventricular arrhythmias
– Most common = AF / AFL
– “Pill in the pocket” dosing
– Increased mortality in patients with CHF and CAD

Availability:
- PO

Toxicity/Pearls:
* 1st line agent for AF in patients without
structural heart disease (CHF, CAD)
* AE’s: GI, CNS (headache, dizziness, fatigue)

Question 7

Propafenone

Answer 7

MOA:
– Strong binding to Na channels –> ↑↑↑ QRS interval
– ↔ action potential duration (APD)
– May also ↑PR interval, ↓contractility

Uses:
– Ventricular & supraventricular arrhythmias
– Most common = AF / AFL
– “Pill in the pocket” dosing
– Increased mortality in patients with CHF and CAD

Availability:
- PO

Toxicity/Pearls:
* Beta blocker properties
* Contraindicated in bronchospastic disease
(asthma, COPD)
* Metallic taste
* Otherwise similar to flecainide