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

Brand names: Tambocor

Used in: Atrial Fibrillation

Flecainide is a class Ic antiarrhythmic used for paroxysmal atrial fibrillation and some supraventricular tachycardias in patients with structurally normal hearts (including as a 'pill-in-the-pocket').

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).

Applies to adults and adolescents 13–17 years. After 3–5 days adjust progressively 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.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION For patients with sustained VT, no matter what their cardiac status, flecainide acetate tablets, like other antiarrhythmics, should be initiated in-hospital with rhythm monitoring. Flecainide has a long half-life (12 to 27 hours in patients). Steady-state plasma levels, in patients with normal renal and hepatic function, may not be achieved until the patient has received 3 to 5 days of therapy at a given dose. Therefore, increases in dosage should be made no more frequently than once every four days, since during the first 2 to 3 days of therapy the optimal effect of a given dose may not be achieved. For patients with PSVT and patients with PAF the recommended …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-01-09. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

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 blocks cardiac sodium channels, slowing conduction; this is antiarrhythmic in normal hearts but proarrhythmic where there is scar or ischaemia.

Prescribing in practice

Avoid in ischaemic or structural heart disease and in significant left-ventricular dysfunction — it increased mortality in such patients (CAST trial).
It is proarrhythmic; in atrial flutter/AF it is usually combined with an AV-nodal blocker to avoid 1:1 conduction.
Reduce the dose in renal or hepatic impairment; levels can be measured where toxicity is suspected.

Monitoring

Confirm a structurally normal heart before use; monitor ECG (QRS widening) and, where relevant, plasma levels.

Counselling the patient

Report palpitations, dizziness or blackouts.
Take it exactly as prescribed; for 'pill-in-the-pocket' use, follow the specific instructions you were given.

Evidence & guidelines

Effective for paroxysmal AF/SVT in structurally normal hearts, but contraindicated in structural/ischaemic heart disease (CAST).

Reference: CAST Trial (NEJM 1989); ESC AF Guidelines 2020; ESC SVT Guidelines 2019; 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.

Calculators

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