Class 1B Antiarrhythmics

Class 1B antiarrhythmics act exclusively on sodium channels and are used in the treatment of ventricular arrhythmias.  Class IB medications shorten the refractory period.  Lidocaine is also used as a local anesthetic.

Class Drugs

• Lidocaine

• Mexiletine

Class Mechanism of Action

Sodium Channel Blockade

• Rapidly associates and dissociates from sodium channels

• Slows phase 0, but less than class IA, WEAK

Shortens phase 3 repolarization

• Related to sustained late sodium channel blockade

Decreases duration of action potential

Class IB Antiarrhythmics Diagram

Class Applications

• Treatment of ventricular arrhythmias

Ventricular fibrillation

• Ventricular tachycardia

• Polymorphic ventricular tachycardia

Class Adverse Effects:

• See individual drug

Drug Table

Drug Name	Application	Comments	Image
Lidocaine	Ventricular Arrhythmias; Local Anesthesia	Adverse Effects; Primarily neurologic:; Nystagmus; Slurred speech; Paresthesias; Agitation; Confusion; Convulsions	"Lid" "Cane"
Mexiletine	Oral Formulation for prevention of ventricular arrhythmias post-MI	Adverse Effects; Nausea, vomiting and dyspepsia most common	"Mexico" "Latrine"