Propafenone

Propafenone is a prescription medication used to treat irregular heartbeat (known medically as arrhythmia). This medication belongs to a group of drugs called Class IC antiarrhythmics which work by blocking sodium channels in the heart, slowing down electrical signals to stabilize heart rhythm.

Propafenone comes in regular tablet and extended-release capsule (Rythmol SR) forms. The tablet is usually taken 3 times daily, every 8 hours. The extended-release capsule is usually taken twice daily, once every 12 hours.

Common side effects include nausea, vomiting, and unusual taste. Propafenone can cause dizziness. Do not drive or operate heavy machinery until you know how it affects you.

CYP2D6 is a protein in your body that is involved in the elimination of propafenone and other drugs from your body. Some patients have less of this protein in their bodies, affecting how much of the drug gets eliminated. Levels of CYP2D6 can vary greatly between individuals, and those having less of this protein are known as "poor metabolizers." 

CYP2D6 testing is done to determine whether you are a poor metabolizer. If you are a poor metabolizer, the levels of propafenone in your blood can become too high. As a result you may be at an increased risk of having more side effects from propafenone. 

Your doctor may adjust your dose of propafenone if you are a poor metabolizer.

Propafenone is a prescription medication used to treat life-threatening, ventricular arrhythmias (irregular heartbeats). Propafenone is also used to correct abnormal heart rate in patients with:

• paroxysmal atrial fibrillation/flutter (PAF) associated with disabling symptoms in patients without structural heart disease.
• paroxysmal supraventricular tachycardia (PSVT) associated with disabling symptoms in patients without structural heart disease.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.

Propafenone may be found in some form under the following brand names:

• Rythmol

• Rythmol SR

Common side effects include:

• unusual taste
• nausea
• vomiting
• dizziness
• constipation
• headache
• fatigue
• blurred vision

This is not a complete list of propafenone side effects. Ask your doctor or pharmacist for more information.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

WARNING: MORTALITY

In the National Heart, Lung and Blood Institute’s Cardiac Arrhythmia Suppression Trial (CAST), a long-term, multi-center, randomized, double-blind study in patients with asymptomatic non-life-threatening ventricular arrhythmias who had a myocardial infarction more than 6 days but less than 2 years previously, an increased rate of death or reversed cardiac arrest rate (7.7%; 56/730) was seen in patients treated with encainide or flecainide (Class IC antiarrhythmics) compared with that seen in patients assigned to placebo (3.0%; 22/725). The average duration of treatment with encainide or flecainide in this study was 10 months.

The applicability of the CAST results to other populations (e.g., those without recent myocardial infarction) or other antiarrhythmic drugs is uncertain, but at present, it is prudent to consider any IC antiarrhythmic to have a significant proarrhythmic risk in patients with structural heart disease. Given the lack of any evidence that these drugs improve survival, antiarrhythmic agents should generally be avoided in patients with non-life-threatening ventricular arrhythmias, even if the patients are experiencing unpleasant, but not life-threatening, symptoms or signs.