Class Ic antiarrhythmic Pregnancy: No evidence of safety in human pregnancy; crosses the placenta — use only if benefit outweighs risk and monitor maternal plasma levels. Excreted in breast milk; use in lactation only if benefit outweighs risk.

Flecainide acetate

Brand names: Tambocor

Flecainide acetate is a class Ic antiarrhythmic used to treat and prevent supraventricular arrhythmias, including paroxysmal atrial fibrillation, and certain ventricular arrhythmias in patients without structural heart disease.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Supraventricular arrhythmias: 50 mg twice daily initially (most patients controlled at this dose). Ventricular arrhythmias: 100 mg twice daily initially.

Route: Oral (take on an empty stomach or one hour before food)

Frequency: Twice daily

Max: Supraventricular arrhythmias: maximum 300 mg daily. Ventricular arrhythmias: maximum 400 mg daily (reserved for patients of large build or where rapid control is required).

Acetate salt — same product SPC as flecainide (Flecainide Acetate 100 mg tablets). Applies to adults and adolescents 13–17 years. After 3–5 days adjust to the lowest level maintaining control. Initiation/dose changes under medical supervision with ECG and plasma-level monitoring. Elderly: max initial 100 mg/day (50 mg twice daily); should not exceed 300 mg/day. Hepatic impairment: do not exceed 100 mg/day. Permanent pacemaker in situ: do not exceed 100 mg twice daily. Not recommended in children under 12 years. NOTE: this SPC is for oral tablets — an IV flecainide formulation also exists (source describes IV-to-oral switch but gives no IV posology here).

Dose adjustments

Renal

Significant renal impairment (creatinine clearance ≤35 mL/min/1.73 m²): maximum initial dose 100 mg/day (50 mg twice daily) with frequent plasma-level monitoring; adjust cautiously after 6–7 days. Severe renal failure may give very slow clearance (half-life 60–70 h).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or excipients
Cardiac failure
History of myocardial infarction with asymptomatic ventricular ectopics or asymptomatic non-sustained ventricular tachycardia
Long-standing atrial fibrillation with no attempt to convert to sinus rhythm
Reduced/impaired ventricular function, cardiogenic shock, severe bradycardia (<50 bpm), severe hypotension
Combination with Class I antiarrhythmic drugs (sodium channel blockers)
Haemodynamically significant valvular heart disease
Sinus node dysfunction, atrial conduction defects, 2nd degree or greater AV block, bundle branch block or distal block (unless pacing rescue is available)
Asymptomatic or mildly symptomatic ventricular arrhythmias
Significant electrolyte imbalance
Known Brugada syndrome

Side effects

Dizziness, vertigo, light-headedness (very common; usually transient)
Visual impairment — diplopia, blurred vision (very common)
Proarrhythmia (common; most likely with structural heart disease)
Hypertension (uncommon)
AV block (2nd/3rd degree), bradycardia, cardiac failure, hypotension (frequency not known)

Interactions

Class I antiarrhythmics (sodium channel blockers) — combination contraindicated
Amiodarone — close monitoring required; dose may need reducing (not to exceed 100 mg twice daily)
Cimetidine — close monitoring required; dose may need reducing (not to exceed 100 mg twice daily)
Drugs causing electrolyte disturbances — correct before/during use (§4.5 not fully present in fetched bundle)

Clinical monograph

How it works

It potently blocks cardiac sodium channels, slowing conduction velocity (phase 0 depolarisation) across atrial, ventricular and accessory-pathway tissue, thereby suppressing re-entrant arrhythmias.

Prescribing in practice

It is contraindicated after myocardial infarction and in significant structural or ischaemic heart disease or impaired left ventricular function because of a proven risk of proarrhythmia and increased mortality.
In atrial flutter or AF it can organise the rhythm and allow rapid 1:1 AV conduction, so co-prescription of an AV-nodal blocking agent is generally advised.
It is negatively inotropic and its clearance is reduced in renal or hepatic impairment, requiring caution and dose review.

Monitoring

Monitor ECG for QRS widening and proarrhythmia, with plasma-level checks in renal impairment or where toxicity is suspected.

Counselling the patient

Report palpitations, blackouts or new dizziness, which may signal a rhythm problem.
Take the dose consistently and do not stop suddenly without advice.
Tell any clinician you take this if your heart is checked or you start new medicines.

Evidence & guidelines

Following the CAST trial, class Ic agents like flecainide are avoided after myocardial infarction and in structural heart disease.

Reference: ESC AF guidelines; NICE NG196; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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