Class IC Agents
The class I antiarrhythmic agents are sodium channel antagonists, with the class IC agents having a slow ion-channel dissociation and classes IA and IB having intermediate and fast dissociation kinetics, respectively. Class IC antiarrhythmic medications are proarrhythmic, and their use should be limited to patients without structural heart disease. The Cardiac Arrhythmia Suppression Trial (CAST) was designed to determine whether the class IC agents encainide, flecainide, and moracizine reduced the incidence of ventricular ectopy and sudden cardiac death after myocardial infarction (MI) in 1,498 patients. However, CAST was discontinued prematurely because of an increased incidence of mortality from arrhythmias, acute MI with shock, or congestive HF in the encainide and flecainide groups. Therefore, the use of class IC agents, including flecainide and propafenone (Table 1), should be limited to patients without left ventricular hypertrophy, CAD, and HF. These agents are generally less efficacious than other antiarrhythmics; approximately 23% of patients maintain normal sinus rhythm at 1 year.
Flecainide is a potent sodium channel blocker that may be used in atrial fibrillation patients without structural heart disease.[1,7] For atrial fibrillation maintenance, flecainide is generally dosed at 50 to 150 mg orally twice daily, with a dose decrease of 50% if the glomerular filtration rate is 50 mL/min or less; plasma levels are monitored closely. It also may be taken as a single oral loading dose of 200 to 300 mg for atrial fibrillation conversion. Plasma levels of flecainide may be monitored in the inpatient setting, with a goal trough level between 0.2 and 1.0 mcg/mL. Common adverse effects include dizziness, tremor, and HF exacerbation. If flecainide is used concomitantly with digoxin, the digoxin dose should be reduced by approximately 25%.
In addition to its sodium channel–blocking activity, propafenone has significant beta-blocking activity that may be beneficial in the management of atrial fibrillation.[1,8] Typical dosing for the immediate-release formulation ranges from 150 to 300 mg orally two to three times daily. The extendedrelease formulation is dosed at 225 to 425 mg orally twice daily. The dose should be reduced in patients with hepatic or renal dysfunction, which will affect propafenone's metabolism and excretion, respectively. Propafenone also may be taken as an oral loading dose of 600 mg for atrial fibrillation conversion. Adverse effects include unusual taste, asthma exacerbation, and dizziness. Digoxin and warfarin doses should be decreased with the use of propafenone.
US Pharmacist. 2013;38(2):20-23. © 2013 Jobson Publishing