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Class IC Antiarrhythmic Pregnancy: Caution — used in fetal tachyarrhythmias via maternal administration; limited data

Flecainide

Brand names: Tambocor

Adult dose

Dose: Oral: 50–100 mg BD. IV cardioversion: 2 mg/kg over 10 min (max 150 mg)
Route: Oral or IV
Frequency: BD (oral); single IV dose for AF cardioversion
Max: 300 mg/day oral; 150 mg IV
For AF/flutter in structurally normal hearts. Pill-in-the-pocket regimen: 200–300 mg single dose for paroxysmal AF. CAST trial: avoid after MI — increased mortality in structural heart disease.

Paediatric dose

Dose: 1 mg/kg
Route: Oral
Frequency: Twice daily (initial; total 2 mg/kg/day in 2 divided doses, increase to 1.5 mg/kg BD if needed)
Max: 100 mg per dose (200 mg/day)
BNFc paediatric SVT/VT — specialist initiation only: child 1 month–11 years 1–3 mg/kg/day in 2–3 divided doses (max 100 mg/dose); child 12–17 years 50 mg BD initially, increased if needed up to 300 mg/day in divided doses. ECG monitoring on initiation; AVOID in structural heart disease (CAST analogues).

Dose adjustments

Renal

Reduce dose by 25–50% in moderate-severe renal impairment (active metabolite accumulates)

Hepatic

Avoid in significant hepatic impairment

Paediatric weight-based calculator

BNFc paediatric SVT/VT — specialist initiation only: child 1 month–11 years 1–3 mg/kg/day in 2–3 divided doses (max 100 mg/dose); child 12–17 years 50 mg BD initially, increased if needed up to 300 mg/day in divided doses. ECG monitoring on initiation; AVOID in structural heart disease (CAST analogues).

Clinical pearls

  • CAST trial (1989): flecainide increased mortality post-MI — only use in structurally NORMAL hearts
  • Pill-in-the-pocket: highly effective self-administration strategy for paroxysmal AF in selected patients
  • Monitor QRS width — widen QRS >25% suggests toxicity, reduce dose
  • Amiodarone halves clearance — if adding amiodarone, reduce flecainide by 50%

Contraindications

  • Structural heart disease (post-MI, HFrEF — CAST trial mortality increase)
  • Sinus node dysfunction or AV block (unless paced)
  • Bundle branch block (or widen QRS >25% of baseline)
  • Electrolyte disturbances

Side effects

  • Dizziness
  • Visual disturbances (blurred vision)
  • Proarrhythmia (VT/VF — rare)
  • Nausea
  • Dyspnoea
  • PR/QRS prolongation

Interactions

  • Amiodarone — doubles flecainide plasma levels (halve flecainide dose)
  • Digoxin — increased digoxin levels
  • Verapamil/diltiazem — increased risk of heart block
  • Propranolol — additive negative inotropic effect

Monitoring

  • ECG (QRS duration, PR interval)
  • Flecainide plasma levels if toxicity suspected
  • Renal function (dose adjustment)
  • Heart rate and rhythm

Reference: BNFc; CAST Trial (NEJM 1989); BNF; ESC AF Guidelines 2020; ESC SVT Guidelines 2019. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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