Medicine & USMLE

Class 1B Antiarrhythmics

Cardio Drugs - Antiarrhythmics
  1. Diltiazem and Verapamil (Calcium Channel Blockers)
  2. Class 1A Antiarrhythmics
  3. Class 1B Antiarrhythmics
  4. Class 1C Antiarrhythmics
  5. Class 3 Antiarrhythmics
  6. Amiodarone Side Effects
  7. Adenosine


Class 1B Antiarrhythmics include the drugs mexiletine, phenytoin, and lidocaine.

These drugs are sodium channel blockers that work by slowing conduction in the heart.

As antiarrhythmics, these medications can be used to treat a variety of ventricular arrhythmias, including PVCs, ventricular fibrillation, and v-tach.

Lidocaine has the potential to cause seizures. Other side effects seen with all class 1B antiarrhythmics include CNS effects, such as confusion and drowsiness. They should also be used with caution in patients with liver damage.

Key Points

  • Class 1B Antiarrhythmics
    • Drug Names
      • Lidocaine (Xylocaine)
      • Mexiletine (Mexitil)
      • Phenytoin (Dilantin)
    • Mechanism
      • Sodium channel blocker
        • Slows conduction
          • Specifically in the atria, ventricles, & His-Purkinje system
          • Slows down the time between each heart contraction
    • Clinical Use
      • Treat ventricular arrhythmias
        • Ventricular tachycardia
        • Ventricular fibrillation
        • Premature ventricular contractions (PVCs)
    • Side Effects
      • Causes drowsiness
      • Causes confusion
        • Monitor mental status and report confusion to the provider
      • Causes seizures (lidocaine)
        • Seizures can often be managed with phenytoin
      • Use with caution with liver damage
        • These drugs are metabolized by the liver, so liver damage will cause the drugs the stay in the bloodstream longer and increases the risk for toxicity