[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antiarrhythmics](https://durgical.com/en/pharmacology/classes/antiarrhythmics/) › Flecainide

# Flecainide

## Antiarrhythmics?

Antiarrhythmics

A class IC sodium channel blocker that keeps sinus rhythm in paroxysmal atrial fibrillation and SVT, but only in hearts without structural disease.

Updated Nov 1, 2026

## Quick facts

**Group**
[Antiarrhythmics](https://durgical.com/en/pharmacology/classes/antiarrhythmics/)

**Target**
Cardiac sodium channel Nav1.5

**Used for**
Prevention of paroxysmal SVT

**Key effects**
Dizziness and lightheadedness · Breathlessness

**Monitor**
ECG · Trough plasma levels in kidney

**ATC**
C01BC04

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

⇅**Cardiac sodium channel Nav1.5**Flecainide

ⓘ The figure shows flecainide in the pore of the rat cardiac sodium channel Nav1.5, very similar to the human channel.

**Target in 3D:** Cardiac sodium channel Nav1.5. PDB structure 6UZ0 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6UZ0) · Drag to rotate · pinch to zoom

Flecainide binds inside the pore of the cardiac sodium channel and unbinds slowly, so it strongly depresses the upstroke of the action potential and slows conduction throughout the heart, most in the His-Purkinje system (wider QRS). It has little effect on repolarisation. It is a negative inotrope.

- Flecainide blocks the Nav1.5 sodium channel and unbinds slowly
- The action potential upstroke slows and the QRS widens
- Slower conduction suppresses re-entry and ectopic beats

## Indications

- Prevention of paroxysmal atrial fibrillation or flutter with disabling symptoms, without structural heart disease [Atrial fibrillation →](https://durgical.com/en/conditions/atrial-fibrillation/)
- Prevention of paroxysmal SVT (AVNRT, AVRT) without structural heart disease [Supraventricular tachycardia (AVNRT, AVRT) →](https://durgical.com/en/conditions/supraventricular-tachycardia/)
- Life-threatening sustained ventricular tachycardia, started in hospital [Ventricular tachycardia →](https://durgical.com/en/conditions/ventricular-tachycardia/)

## Adverse effects

### Common

- Dizziness and lightheadedness
- Blurred vision or trouble focusing
- Breathlessness
- Headache, nausea and tremor

### Serious (rare, important)

- New or worse ventricular arrhythmias (proarrhythmia), with higher mortality after myocardial infarction
- Atrial flutter with 1:1 conduction and a very fast ventricular rate
- New or worse heart failure
- Conduction block and higher pacing thresholds

## Contraindications

- Recent myocardial infarction or structural heart disease (CAST)
- Second- or third-degree AV block, or bifascicular block, without a pacemaker
- Cardiogenic shock

## Key interactions

**Amiodarone**
Flecainide levels can double; the dose is reduced and levels followed

**Digoxin**
Small rise in digoxin levels

**Propranolol and other beta blockers**
Both levels rise slightly and negative inotropic effects add up

**CYP2D6 inhibitors such as quinidine**
Higher flecainide levels

## What is monitored

- ECG: QRS width and PR interval
- Trough plasma levels in kidney or liver disease or with amiodarone
- Pacing threshold in patients with pacemakers
- Signs of heart failure

## Administration and safety

- Not started in patients with a previous infarction or a weak, scarred ventricle.
- In atrial fibrillation or flutter it is usually combined with an AV nodal blocker (beta blocker or non-dihydropyridine calcium channel blocker).
- For sustained ventricular tachycardia it is started in hospital with ECG monitoring.

## Pregnancy and breastfeeding

It caused malformations in one rabbit strain and human data are limited, so it is used in pregnancy only if the benefit justifies the risk.

## Nursing care

- Check pulse and ECG; report QRS widening, new palpitations or fainting.
- Ask about breathlessness, swelling or weight gain (heart failure).
- Teach the patient to report visual blurring or dizziness, and not to stop or double doses.

## Pharmacokinetics

**Absorption**
Nearly complete by mouth, with no significant first-pass effect

**Metabolism**
Liver (CYP2D6), partly to a weakly active metabolite

**Elimination**
Kidneys, partly unchanged; elimination slows with kidney failure and very alkaline urine

**Half-life**
Long (around a day), so steady state takes several days

## Memory aid

IC = I Can't use it in a Cracked (scarred) heart: flecainide is for structurally normal hearts only.

## Test yourself

Think of the answer, then tap the question to see it.

## What did the CAST trial show about flecainide?

In patients after myocardial infarction with non-life-threatening ventricular ectopy, flecainide increased mortality and arrests.

## Why is flecainide combined with an AV nodal blocker in atrial flutter?

By slowing the flutter rate it can allow 1:1 AV conduction and a very fast ventricular rate.

## Which ECG interval is watched most closely with flecainide?

The QRS duration, which widens as sodium channels are blocked.

## What happens to flecainide levels when amiodarone is added?

They can double, so the flecainide dose is reduced and plasma levels monitored.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/flecainide/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 4

- [Propafenone](https://durgical.com/en/pharmacology/propafenone/)
- [Amiodarone](https://durgical.com/en/pharmacology/amiodarone/)
- [Metoprolol](https://durgical.com/en/pharmacology/metoprolol/)
- [Verapamil](https://durgical.com/en/pharmacology/verapamil/)

## Related conditions 3

- [Atrial fibrillation](https://durgical.com/en/conditions/atrial-fibrillation/)
- [Supraventricular tachycardia (AVNRT, AVRT)](https://durgical.com/en/conditions/supraventricular-tachycardia/)
- [Ventricular tachycardia](https://durgical.com/en/conditions/ventricular-tachycardia/)

[← Back to the class: Antiarrhythmics](https://durgical.com/en/pharmacology/classes/antiarrhythmics/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - FLECAINIDE ACETATE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee9595d5-08a1-4529-9215-ddc3c7f929c4) (DailyMed (U.S. National Library of Medicine), 2026); [Flecainide: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a608040.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C01BC04) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [6UZ0: Cardiac sodium channel with flecainide](https://www.rcsb.org/structure/6UZ0) (RCSB Protein Data Bank, 2020).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/flecainide/
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