Class IC antiarrhythmics

Class IC antiarrhythmics

Class IC antiarrhythmics are used to treat certain severe, refractory (resistant) ventricular arrhythmias. Class IC antiarrhythmics include:

• flecainide
• moricizine
• propafenone.

Pharmacokinetics

After oral administration, class IC antiarrhythmics are absorbed well, distributed in varying degrees, and probably metabolized by the liver. They’re excreted primarily by the kidneys, except for propafenone, which is excreted primarily in stool.

 

Memory jogger

To remember the main differences between what Class IA, Class IB, and Class IC antiarrhythmics do, just think of their names:

Class IA: Alters the myocardial cell membrane

Class IB: Blocks the rapid influx of sodium ions

Class IC: slows Conduction

More about moricizine

After oral administration, about 38% of moricizine is absorbed. It undergoes extensive metabolism, with less than 1% of a dose excreted unchanged in the urine. Moricizine is highly protein-bound, leaving only a small portion of the drug free to produce its antiarrhythmic effect.

 

Pharmacodynamics

Class IC antiarrhythmics primarily slow conduction along the heart’s conduction system. Moricizine decreases the fast inward current of sodium ions of the action potential, depressing the depolarization rate and the effective refractory period.

 

Pharmacotherapeutics

Like class IB antiarrhythmics, class IC antiarrhythmics are used to treat and prevent life-threatening ventricular arrhythmias. They’re also used to treat supraventricular arrhythmias (abnormal heart rhythms that originate above the bundle branches of the heart’s conduction system).

Flecainide and propafenone may also be used to prevent paroxysmal supraventricular tachycardia (PSVT) in patients without structural heart disease. Moricizine is used to manage life-threatening ventricular arrhythmias such as sustained ventricular tachycardia.

 

Drug interactions

Class IC antiarrhythmics may exhibit additive effects with other antiarrhythmics. Other interactions include the following:

Warning!

Adverse reactions to class IC antiarrhythmics

Class IC antiarrhythmics can produce serious adverse reactions, including the development of new arrhythmias and aggravation of existing arrhythmias. They’re avoided in patients with structural heart defects because of a high incidence of mortality.

Because propafenone has beta-blocking properties, it may cause bronchospasm.

Adverse reactions to moricizine

The most serious adverse reaction is the appearance of new arrhythmias or the worsening of an existing arrhythmia.

Other cardiovascular adverse reactions include palpitations, shortness of breath, chest pain, heart failure, and cardiac arrest.

GI adverse reactions include abdominal pain, heartburn, nausea, and vomiting.

• When used with digoxin, flecainide and propafenone increase the risk of digoxin toxicity.
• Propafenone increases plasma concentrations of warfarin and increases prothrombin times.
• Quinidine increases the effects of propafenone.
• Cimetidine may increase the plasma level and the risk of toxicity of moricizine.
• Propanolol or digoxin given with moricizine may increase the PR interval on the electrocardiogram.
• Theophylline levels may be reduced in a patient receiving moricizine.
• Ritonavir increases the plasma concentration and the effects of propafenone.
• Propafenone increases the serum concentration and the effects of metoprolol and propranolol.