CLASS IB/ CLASS IC

What is the prototype Class IB sodium channel blocker?

Lidocaine (Xylocaine)

What is the mechanism of action for Class IB sodium channel blockers like Lidocaine?

Shortens the repolarization phase (Phase 3) of the cardiac action potential and raises the stimulation threshold in the ventricles.

What are the primary uses of Lidocaine?

Serious ventricular dysrhythmias, especially during Acute MI, cardiac surgery, cardiac catheterization, and digitalis toxicity.

Lidocaine is not used for?

Atrial dysrhythmias

What is the duration of action for IV Lidocaine?

10–20 minutes.

What are the therapeutic and toxic levels of Lidocaine?

Therapeutic level: 1.5–5 mcg/mL; Toxic level: >6 mcg/mL.

What contraindications exist for using Lidocaine?

Allergy to Lidocaine or amide-type local anesthetics and must not be used with epinephrine in IV form.

What are some adverse effects of Lidocaine usage?

CNS toxicity (confusion, tremors, seizures), hypotension, bradycardia, cardiovascular collapse in severe overdose.

What monitoring is essential for patients receiving Lidocaine?

Monitor ECG continuously during therapy and ensure liver function is adequate.

What are the Class IC sodium channel blockers mentioned in the notes?

Flecainide and Propafenone (Rythmol SR).

What is a major concern when using Flecainide?

Increased risk of nonfatal cardiac arrest or death in patients with recent myocardial infarction or chronic atrial fibrillation.

What distinguishes Class IB from Class IC sodium channel blockers regarding action?

Class IB shortens repolarization; Class IC strongly blocks sodium channels with no effect on repolarization.

Why should Class IC drugs like Flecainide be initiated only in a hospital?

They require continuous ECG monitoring due to the risk of causing or worsening dysrhythmias.

What is the mechanism of action for Class IC sodium channel blockers?

They profoundly slow conduction in the ventricles without affecting the refractory period.

What is the major risk associated with Class IC sodium channel blockers?

Prodysrhythmia, which can lead to V-fib or sustained VT.

What is the effect of Lidocaine on atrial tissue?

Minimal effect on atrial tissue.

What specific precaution should be taken when administering IV Lidocaine?

Administer IV bolus over 45–90 seconds to prevent toxicity.