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Flecainide: Arrhythmia Uses, Warnings, Side Effects, Dosage

Generic Name: flecainide

Brand and Other Names: flecainide acetate, Tambocor (discontinued brand)

Drug Class: Antidysrhythmics, IC

What is flecainide, and what is it used for?

Flecainide is a medication used to prevent and treat certain heart rhythm disorders (arrhythmias) which cause abnormally rapid heart rates that can be sometimes life-threatening.

Flecainide is a medication that belongs to class IC antidysrhythmics, one of the many drug classes used in the treatment of cardiac arrhythmias. Flecainide works by slowing down the conduction of electrical signals in the heart.

The heart’s electrical activity is regulated by specialized heart muscle tissue in the right atrium known as the sinoatrial (SA) node, the heart’s natural pacemaker. The SA node generates electrical impulses at a regular rhythm to make the heart chambers contract in coordination to pump blood. The impulses make the atria contract first and the atrioventricular (AV) node delays the signal till the atrial blood empties into the ventricles. The impulses then travel through nerve fibers to make the ventricles contract and pump out the collected blood.

Abnormal functioning of the cardiac electrical circuit can cause rapid and irregular signals that result in uncoordinated contractions of the heart chambers. This can overwork the heart, impair the flow of blood which can pool up increasing the risk for clot formation, stroke, heart failure or other life-threatening conditions.

Flecainide inhibits the action of sodium and potassium ion channels in the heart, which works in the following ways to slow down heart conduction rate and correct abnormal rhythms:

  • Increases the threshold for depolarization and the rate of action potential
  • Prolongs the refractory period and the action potential duration in both atrial and ventricular muscle fibers

Flecainide is FDA-approved for the prevention of the following type of arrhythmias in patients without structural heart disease:

Off-label uses in adults include:


Flecainide can cause new onset or worsening of arrhythmia and its use should be reserved for patients in whom the benefits of treatment outweigh the risks.

Flecainide use should be restricted to life-threatening ventricular arrhythmias, and not prescribed for less severe ventricular arrhythmias. Flecainide has known proarrhythmic properties and there is lack of evidence of improved survival with flecainide.

Do not use flecainide in patients with chronic atrial fibrillation or recent myocardial infarction (MI).

Do not use in patients hypersensitive to flecainide or any of its components.

Do not use flecainide in patients with following conditions:

  • Structural heart disease
  • Pre-existing second or third-degree atrioventricular (AV) block
  • Right bundle branch block when associated with a left hemiblock (bifascicular block), except in patients with a functioning artificial pacemaker
  • Cardiogenic shock

Use flecainide with caution in patients with atrial fibrillation, congestive heart failure (CHF), hypertension, hypotension or sick sinus syndrome.

Use with caution in elderly patients and post MI patients.

Manage patients with lowest effective dose to avoid proarrhythmic effects.

Use with caution in patients with permanent pacemakers or temporary pacing wires, flecainide can increase endocardial pacing thresholds and suppress ventricular escape rhythms.

Use with caution in patients with liver or kidney impairment.

Correct electrolyte imbalances, particularly low potassium (hypokalemia) and low magnesium (hypomagnesemia) before starting flecainide therapy.

Flecainide may cause visual disturbances.

Use with caution in pediatric patients, small changes in dose may lead to disproportionate increases in plasma concentrations of flecainide.

Discontinuation of flecainide should be done in the hospital.


In the U.S., 1 in every 4 deaths is caused by heart disease.
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What are the side effects of flecainide?

Common side effects of flecainide include:

Less common side effects of flecainide include:

Infrequent and rare side effects of flecainide include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

  • Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
  • Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
  • Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
  • Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

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What are the dosages of flecainide?


  • 50 mg
  • 100 mg
  • 150 mg


Arrhythmias (Prevention)

PSVT and paroxysmal atrial fibrillation

  • 50 mg orally twice daily; may increase by 50 mg every 4 days; do not exceed 300 mg/day

Sustained VT

  • 100 mg orally twice daily initiated in hospital; may increase by 50 mg every 4 days; do not exceed 400 mg/day



  • Infants under 6 months: 50 mg/m²/day orally divided every 8-12 hours
  • Infants 6 months or older: 100 mg/m²/day orally divided every 8-12 hours
  • Not to exceed 200 mg/m²/day
  • Usual therapeutic level: 200-500 ng/ml; some may require under 800 ng/ml for adequate control

Dosing considerations

  • Steady-state plasma levels not achieved for 3-5 days, so increases in dosage should not be made less than every 4 days
  • Loading dose not recommended, due to increased incidence of proarrhythmic events and chronic heart failure
  • Patients intolerant to twice-daily dosing may require 8 hour dosing
  • Once adequate control of arrhythmia has been achieved, may reduce dose, provided there is no loss of efficacy
  • After 5 doses/steady-state, obtain ECG after initiation or change of dose; obtain plasma trough flecainide levels 1 hour pre-dose
  • Usual trough plasma levels: 0.2-1 mcg/mL
  • When given concomitantly with amiodarone, reduce flecainide dose by 50% and monitor closely
  • Dose cautiously in patients with history of heart attack (myocardial infarction) or chronic heart failure
  • When switching from another antiarrhythmic to flecainide, allow over 2-4 plasma half-lives to elapse before starting flecainide; if discontinuation of previous drug may produce life-threatening arrhythmias, consider hospitalizing the patient

Dosage Modifications

Renal impairment

  • Severe (under 35 ml/min): 100 mg orally once daily or 50 mg orally twice daily
  • Higher than 25 ml/min: 100 mg orally twice daily

Hepatic impairment

  • Use only if benefits outweigh risks; monitor plasma levels regularly; reduce dose as necessary


  • Flecainide overdose may cause abnormal heart rhythms, reduced heart rate and contraction force, and hypotension that can result in death.
  • Overdose is treated with supportive and symptomatic care, which may include administration of medications to increase heart contractility, respiratory and circulatory assistance, and acidification of urine.

What drugs interact with flecainide?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

  • Severe interactions of flecainide include:
    • nirmatrelvir
    • nirmatrelvir/ritonavir
    • tipranavir
  • Flecainide has serious interactions with at least 63 different drugs.
  • Flecainide has moderate interactions with at least 133 different drugs.
  • Mild interactions of flecainide include:

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • Untreated arrhythmia in pregnancy can lead to maternal and fetal adverse outcomes.
  • The lowest effective dose of flecainide may be used with caution for ongoing management of pregnant women with highly symptomatic supraventricular tachycardia.
  • Avoid flecainide use during first trimester if possible.
  • Flecainide is present in breast milk, use with caution in nursing mothers.

What else should I know about flecainide?

  • Take flecainide exactly as prescribed. Overdose can be fatal.
  • In case of overdose, seek immediate medical help or contact Poison Control.
  • Store flecainide safely out of reach of children.

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