Class IC antiarrhythmics
Class IC antiarrhythmics
are used to treat
certain severe, refrac-tory (resistant) ventricular arrhythmias. Class IC
antiarrhythmics include:
·
flecainide
·
moricizine
·
propafenone.
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.)
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