Flecainide

Pronunciation: fleh-KAY-nide.

Generic name
Flecainide acetate
Drug class
Class Ic antiarrhythmic (cardiac sodium-channel blocker)
Form
Tablet (50mg, 100mg, and 150mg depending on market); controlled-release capsule (100mg, 200mg, 300mg, New Zealand); oral solution (some markets)
Route
Oral (tablet, controlled-release capsule where available, or oral solution)
Legal status
Prescription-only medicine, live-confirmed as currently authorised in the United States, United Kingdom, Canada, Australia, and New Zealand. European Union authorisation status could not be independently confirmed this session (EMA's search tool did not render a usable result), though flecainide is a long-established generic typically authorised via national procedures across the EU.

Availability and supply rules vary by country

Trade names by country: Canada

Australia: · Full directory

What Flecainide acetate is and how it works

Flecainide is a Class Ic antiarrhythmic medicine used to treat specific heart-rhythm problems, including paroxysmal supraventricular tachycardia, Wolff-Parkinson-White syndrome, AV nodal re-entrant tachycardia, and paroxysmal atrial fibrillation or flutter in people without structural heart disease. It is also used, under specialist hospital supervision, for genuinely life-threatening ventricular arrhythmias when the potential benefit is judged to outweigh its risks. (9) (1) (2)

Flecainide has a real, well-documented, and serious safety history: a landmark trial (CAST) found that using flecainide (and a related medicine, encainide) to suppress mild, symptom-free extra heartbeats after a heart attack actually increased the risk of death, rather than reducing it. Because of this, flecainide is only used in people who have been carefully assessed to confirm they do not have structural heart disease, a weakened heart muscle, or significant coronary artery disease -- and, when used for life-threatening rhythm problems, only under specialist cardiology supervision with careful monitoring. This is not a medicine to start, stop, or adjust without a cardiologist's direct involvement.

Mechanism of action: how Flecainide acetate works

Flecainide is a Class Ic antiarrhythmic that potently blocks the fast cardiac sodium current (INa), slowing conduction velocity throughout the heart, particularly in the His-Purkinje system, which widens the QRS complex on ECG. It also affects potassium rectifier currents and ryanodine-receptor-mediated calcium release. It has a narrow therapeutic index. (8)

What Flecainide acetate is used for

Paroxysmal supraventricular tachycardia, Wolff-Parkinson-White syndrome, and AV nodal re-entrant tachycardia

Flecainide is used to prevent or treat these specific fast-heart-rhythm conditions in people without structural heart disease. (8) (1)

Paroxysmal atrial fibrillation and atrial flutter with disabling symptoms (without structural heart disease)

Used to prevent recurrent episodes of paroxysmal atrial fibrillation/flutter causing disabling symptoms, specifically in people confirmed not to have structural heart disease. Not recommended for chronic (ongoing/permanent) atrial fibrillation. (2) (3) (5)

Life-threatening ventricular arrhythmias (specialist hospital-initiated)

Used for genuinely life-threatening ventricular arrhythmias when specialist assessment concludes the benefit outweighs the well-documented mortality risk seen in the CAST trial. Initiation requires hospital admission and specialist cardiology oversight. (8) (1)

Off-label specialist uses, including fetal supraventricular tachycardia

Reported off-label uses in the medical literature include Long QT syndrome type 3, catecholaminergic polymorphic ventricular tachycardia (combined with beta-blockers), Andersen-Tawil syndrome type 1, and fetal supraventricular tachycardia -- all specialist-directed uses, not routine or self-selected treatment. (8)

Before taking Flecainide acetate

Do not take / not appropriate for

  • Do not take flecainide if you have structural heart disease, a weakened heart muscle, significant coronary artery disease, or heart failure -- this is the central, CAST-trial-driven restriction on this medicine. (all countries) (2) (9)
  • Do not take flecainide if you have cardiogenic shock, pre-existing second- or third-degree heart block, or right bundle branch block with left hemiblock, unless you have a pacemaker to maintain your heart rhythm. (all countries) (1)
  • Do not take flecainide if you have Brugada syndrome, significant valvular heart disease, severe bradycardia (heart rate under 50 beats per minute), or severe low blood pressure. (United Kingdom (SmPC-listed contraindications; consistent with the class-wide safety profile)) (2)
  • Do not combine flecainide with another Class I antiarrhythmic medicine. (all countries) (2)
  • Flecainide is not recommended for chronic (ongoing/permanent) atrial fibrillation. (all countries) (3) (5)

Tell your clinician about

  • Any history of heart attack, heart failure, coronary artery disease, or a weakened heart muscle -- this determines whether flecainide is appropriate for you at all.
  • Any personal or family history of Brugada syndrome or unexplained sudden cardiac death, since flecainide can unmask Brugada syndrome.
  • Any kidney or liver problems, since these affect how flecainide is cleared from your body and how your dose is monitored.
  • All other medicines you take, especially other antiarrhythmics, beta-blockers, digoxin, or medicines affecting the same liver enzyme pathway.
  • Whether you are pregnant, planning pregnancy, or breastfeeding.
(2) (8)

How to take Flecainide acetate

  • Flecainide is started and adjusted by a cardiologist or heart-rhythm specialist, typically with baseline heart tracing (ECG), heart imaging, and exercise testing beforehand, and continued ECG monitoring during treatment.
  • Take exactly as prescribed and at the same times each day -- this medicine has a narrow therapeutic index, meaning the difference between an effective dose and a harmful one can be small.
  • Never change your dose, or begin or continue this medicine, without your prescribing clinician's direct involvement.
(1) (2)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (8) (9)

Missed dose

Contact your prescribing clinician or pharmacist for specific guidance on a missed dose rather than guessing, given this medicine's narrow therapeutic index and the importance of maintaining a consistent blood level.

Overdose

Flecainide overdose is a genuine medical emergency because of its effects on heart rhythm and conduction. Seek emergency medical help immediately for a suspected overdose, or if you notice fainting, severe dizziness, a very slow or irregular heartbeat, or difficulty breathing. (8) (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Dizziness, visual disturbances (such as blurred or double vision), and shortness of breath have been commonly reported.

What to notice: Dizziness, visual disturbances (such as blurred or double vision), and shortness of breath have been commonly reported.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Nausea and headache have also been reported.

What to notice: Nausea and headache have also been reported.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Serious warnings

Worsening or new heart rhythm problems (pro-arrhythmia), including in people with structural heart disease — boxed_warning

Symptoms: New or worsening palpitations, fainting, severe dizziness, or a very fast, slow, or irregular heartbeat.

Action: Seek emergency medical help immediately for any of these symptoms. This risk is the reason flecainide is restricted to people without structural heart disease outside of specialist-supervised, life-threatening arrhythmia treatment -- the CAST trial found this exact risk translated into a real increase in death when flecainide was used in the wrong patient population. (9) (2)

Unmasking of Brugada syndrome — high caution

Symptoms: Fainting, seizure-like activity, or cardiac arrest can be the first sign in someone with previously undiagnosed Brugada syndrome.

Action: Tell your clinician about any personal or family history of unexplained fainting or sudden cardiac death before starting flecainide, since the medicine itself can reveal this underlying, genetically-linked heart rhythm condition. (2)

Paradoxical increase in ventricular rate when treating atrial flutter — high caution

Symptoms: A faster, not slower, heartbeat after starting treatment for atrial flutter -- the opposite of the intended effect.

Action: This is a recognised risk, particularly with intravenous flecainide, caused by the medicine slowing the atrial flutter rate enough that more of those beats are conducted to the ventricles. It is why specialist consultation is recommended before emergency use, and why combining with a rate-controlling medicine such as digoxin or a beta-blocker is sometimes used under specialist direction. (6)

Signs of a serious allergic reaction — emergency

Symptoms: Swelling of the face, lips, tongue, or throat; difficulty breathing; widespread rash or hives.

Action: Seek emergency medical help immediately. (1)

Interactions

  • Other Class I antiarrhythmic medicines: combining with flecainide is not done, because of additive pro-arrhythmic risk. (2)
  • Beta-blockers: can be combined under specialist supervision (for example, to manage atrial flutter conduction risk), but the combination needs careful monitoring because of additive effects on heart rate and contraction strength. (6)
  • Digoxin: has been used alongside flecainide under specialist direction, particularly to help manage the paradoxical ventricular rate risk in atrial flutter. (6)
  • Medicines that affect the same liver enzyme pathway used to clear flecainide can raise or lower its blood levels -- disclose your full medicine list to your clinician or pharmacist. (8)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Flecainide is used off-label for fetal supraventricular tachycardia under specialist fetal-medicine supervision. Teratogenic and embryotoxic effects were seen in one rabbit strain at doses around 4 times the usual human dose (not seen in other animal species tested at similar doses) -- this is animal-study data, not a confirmed human finding, but any use in pregnancy should be specialist-directed. (1) (2) (3) (4) (5) (6) (8) (9)

Breastfeeding

No specific breastfeeding safety data was independently verified this session; discuss with a specialist before use while breastfeeding. (1) (2) (3) (4) (5) (6) (8) (9)

Children

Not approved for children in the sources reviewed; any pediatric use requires hospital initiation with cardiologist oversight, given reported cases of serious cardiac events in children with structural heart disease. (1) (2) (3) (4) (5) (6) (8) (9)

Elderly

Generally started at a lower dose, with a lower maximum daily dose in some markets, reflecting reduced clearance and higher sensitivity to pro-arrhythmic effects. (1) (2) (3) (4) (5) (6) (8) (9)

Hepatic_impairment

Flecainide is partly cleared by the liver; impaired hepatic function can raise blood levels, so specialist dose adjustment and monitoring are used. (1) (2) (3) (4) (5) (6) (8) (9)

Renal_impairment

Significant kidney impairment requires a lower starting dose and frequent blood-level monitoring, since flecainide is also cleared by the kidneys. (1) (2) (3) (4) (5) (6) (8) (9)

Source_ids

US-DAILYMED-FLECAINIDE-2026,GENERAL-FLECAINIDE-STATPEARLS-2026,NZ-MEDSAFE-TAMBOCOR-DATASHEET-2026 (1) (2) (3) (4) (5) (6) (8) (9)

Monitoring

Before starting

  • Baseline ECG to assess QRS duration and rule out conduction disease
  • Heart imaging (e.g. echocardiogram) to confirm absence of structural heart disease
  • Exercise stress testing in some cases
  • Screening for sinus node or AV node disease
  • Kidney and liver function assessment

During treatment

  • Regular ECG monitoring for QRS widening -- a dose reduction is typically considered if the QRS interval increases by more than about 25%.
  • Periodic blood pressure and general cardiac monitoring.
  • Blood level monitoring, particularly in kidney or liver impairment, given the narrow therapeutic index (target trough range approximately 0.2-1.0 mcg/mL in the evidence reviewed).
(8)

Storage

Store at room temperature, away from moisture and light, out of reach of children, per the specific product label.

Study the drug class: Class I antiarrhythmics

Professional information

Clinician-facing context only. This section reflects the FDA label, UK SmPC, Health Canada monograph, and peer-reviewed CAST trial literature reviewed for this page.

United States

Indication: PSVT/paroxysmal AF; sustained VT; life-threatening ventricular arrhythmias (hospital-initiated)

Dose summary: PSVT/PAF: 50mg twice daily, max 300mg/day. VT: 100mg twice daily, max 400mg/day. Severe renal impairment: 100mg once daily (or 50mg twice daily), with frequent plasma-level monitoring.

Renal context: Reduced starting dose and frequent plasma-level monitoring required for creatinine clearance <=35 mL/min/1.73m2. (1)

United Kingdom

Indication: AVNRT/WPW-associated arrhythmias; severe symptomatic ventricular arrhythmias unresponsive to other therapy; paroxysmal atrial arrhythmias with disabling symptoms

Dose summary: Supraventricular arrhythmias: 50mg twice daily, max 300mg/day. Ventricular arrhythmias: 100mg twice daily, max 400mg/day. Elderly: generally not exceeding 100mg initial dose or 300mg/day total.

Renal context: Caution and dose adjustment required in renal impairment given renal elimination. (2)

Canada

Indication: Similar supraventricular/ventricular arrhythmia indications; not recommended for chronic atrial fibrillation

Dose summary: Per product monograph; reduced ventricular function (EF<40%) and/or ischaemic heart disease noted as increasing cardiac adverse-reaction risk.

Renal context: Dose adjustment required in renal impairment given renal elimination. (3)

Mechanism of action

Hepatic guidance

Partly hepatically metabolised; impaired hepatic function can raise blood levels, requiring specialist dose adjustment and monitoring.

Overdose note

No specific antidote; overdose management is supportive and typically requires intensive cardiac monitoring/care given the risk of severe conduction abnormalities and arrhythmia. (8)

Frequently asked questions

Why does flecainide have a boxed warning about death risk?

Because of a landmark study, the Cardiac Arrhythmia Suppression Trial (CAST). It tested whether suppressing mild, symptom-free extra heartbeats after a heart attack with flecainide (and a related medicine, encainide) would prevent sudden death. Instead, people taking flecainide had a higher death/cardiac-arrest rate (5.1%) than those on placebo (2.3%) over about 10 months, and the trial's flecainide and encainide arms were stopped early in 1989 as a result. This is why flecainide is now restricted to people without structural heart disease, except for genuinely life-threatening rhythm problems under specialist supervision. (1) (9)

Who should not take flecainide?

People with structural heart disease, a weakened heart muscle, significant coronary artery disease, heart failure, a recent heart attack, certain heart block conditions (without a pacemaker), cardiogenic shock, or Brugada syndrome should not take flecainide, based on the CAST trial finding and consistent regulator guidance across the markets reviewed. It is also not recommended for chronic (ongoing) atrial fibrillation. (2) (9) (3)

Is flecainide used in pregnancy or for babies?

Flecainide is used off-label, under specialist fetal-medicine supervision, to treat a fast heart rhythm in an unborn baby (fetal supraventricular tachycardia). It is not approved for children in the sources reviewed, and any pediatric use requires hospital initiation with cardiologist oversight, given reported serious cardiac events in children with structural heart disease. (8)

Can flecainide make a heart rhythm problem worse instead of better?

Yes -- this is a real, documented risk (pro-arrhythmia), and it is precisely what the CAST trial demonstrated when flecainide was used in the wrong patient population. There is also a specific, separate risk when treating atrial flutter: flecainide can paradoxically cause a faster ventricular heart rate rather than a slower one, particularly with intravenous use, which is why specialist consultation is recommended before emergency use. (9) (6)

What is the mechanism of action of Flecainide acetate?

Flecainide is a Class Ic antiarrhythmic that potently blocks the fast cardiac sodium current (INa), slowing conduction velocity throughout the heart, particularly in the His-Purkinje system, which widens the QRS complex on ECG. It also affects potassium rectifier currents and ryanodine-receptor-mediated calcium release. It has a narrow therapeutic index. (8)

What is the generic name of Flecainide?

The generic name is Flecainide acetate. (8) (1)

What class of drug is Flecainide acetate?

Flecainide is classed as: Class Ic antiarrhythmic (cardiac sodium-channel blocker). (8) (1)

References

  1. FLECAINIDE ACETATE tablet -- FDA labelDailyMed (U.S. National Library of Medicine) -- FDA-approved product label · United States · accessed 2026-07-30 · source 1
  2. Flecainide Acetate 50 mg tablets -- Summary of Product Characteristics (SmPC)electronic medicines compendium (emc), United Kingdom -- Summary of Product Characteristics (SmPC), Milpharm Limited · United Kingdom · accessed 2026-07-30 · source 2
  3. TAMBOCOR (flecainide acetate) Tablets 50 and 100mg -- Product MonographHealth Canada -- Product Monograph, Tambocor / APO-Flecainide · Canada · accessed 2026-07-30 · source 3
  4. TGA PI & CMI search for 'flecainide' -- 10 documents availableTherapeutic Goods Administration (TGA), Australia -- PI & CMI product search · Australia · accessed 2026-07-30 · source 4
  5. TAMBOCOR Tablets / TAMBOCOR CR Capsules -- New Zealand Data SheetMedsafe (New Zealand regulator) -- approved New Zealand Data Sheet · New Zealand · accessed 2026-07-30 · source 5
  6. Cardiac risks associated with flecainideMedsafe (New Zealand regulator) -- Prescriber Update safety article · New Zealand · accessed 2026-07-30 · source 6
  7. EMA medicine search for 'flecainide' -- inconclusive (JavaScript-driven search tool)n/a -- disclosed live-query limitation, not a confirmed negative or positive centralised-procedure result · European Union · accessed 2026-07-30 · source 7
  8. FlecainideStatPearls (NCBI Bookshelf) -- peer-reviewed clinical reference · General/international clinical background · accessed 2026-07-30 · source 8
  9. Mortality and Morbidity in Patients Receiving Encainide, Flecainide, or Placebo: The Cardiac Arrhythmia Suppression TrialNew England Journal of Medicine -- original CAST investigators' publication · General/international clinical evidence (US-based multicentre trial) · accessed 2026-07-30 · source 9

Brand names by country

Single-ingredient Flecainide acetate names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

Canada

  • TAMBOCOR
View brands in additional countries.

This page provides general reference information about flecainide and is not a substitute for advice from a cardiologist or doctor. Flecainide has a real, serious mortality-risk history in people with structural heart disease and requires specialist assessment and monitoring -- it must never be started, stopped, or adjusted without direct specialist involvement.

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