Class IC antiarrhythmics
Class IC antiarrhythmics are used to treat certain severe, refrac-tory (resistant) ventricular arrhythmias. Class IC antiarrhythmics include:
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.
After oral administration, about 38% of moricizine is absorbed. It undergoes extensive metabolism, with less than 1% of a dose ex-creted unchanged in the urine. Moricizine is highly protein-bound, leaving only a small portion of the drug free to produce its antiar-rhythmic effect.
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 de-polarization rate and the effective refractory period.
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 with-out structural heart disease. Moricizine is used to manage life-threatening ventricular arrhythmias such as sustained ventricular tachycardia.
Class IC antiarrhythmics may exhibit additive effects with other antiarrhythmics. Other interactions include the following:
· 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 toxici-ty 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 mori-cizine.
· Ritonavir increases the plasma concentration and the effects of propafenone.
· Propafenone increases the serum concentration and the effects of metoprolol and propranolol. (See Adverse reactions to class ICantiarrhythmics.)