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.
Quick facts
- Group
- 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.
Mechanism of action
The figure shows flecainide in the pore of the rat cardiac sodium channel Nav1.5, very similar to the human channel.
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 →
- Prevention of paroxysmal SVT (AVNRT, AVRT) without structural heart disease Supraventricular tachycardia (AVNRT, AVRT) →
- Life-threatening sustained ventricular tachycardia, started in hospital Ventricular tachycardia →
Adverse effects
Common
- Dizziness and lightheadedness
- Blurred vision or trouble focusing
- Breathlessness
- Headache, nausea and tremor
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
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.
Connections
← Back to the class: 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 (DailyMed (U.S. National Library of Medicine), 2026); Flecainide: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); 6UZ0: Cardiac sodium channel with flecainide (RCSB Protein Data Bank, 2020).
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Representative model, for educational purposes only.