What is the recommended dosage of Flecainide (Anti-arrhythmic medication) Acetate 100MG Oral Tablet for adults with paroxysmal supraventricular tachycardia or paroxysmal atrial fibrillation?

Flecainide Acetate 100mg Oral Tablet Dosage for Paroxysmal Supraventricular Tachycardia and Paroxysmal Atrial Fibrillation

For adults with paroxysmal supraventricular tachycardia (PSVT) or paroxysmal atrial fibrillation (PAF), start flecainide at 50 mg every 12 hours, and increase by 50 mg twice daily every 4 days as needed for efficacy, with a maximum dose of 300 mg/day (150 mg twice daily). 1

Initial Dosing

• Starting dose: 50 mg every 12 hours for both PSVT and PAF patients 1
• This conservative starting approach minimizes the risk of proarrhythmic events and congestive heart failure, which are more common with higher initial doses 1

Dose Titration

• Increase by 50 mg twice daily (100 mg/day total) every 4 days until efficacy is achieved 1
• The 4-day interval is critical because flecainide has a long half-life (12-27 hours), and steady-state plasma levels may not be reached for 3-5 days 1
• Dose escalation should occur only after assessing response at the current dose for at least 4 days 1

Maximum Dosing

• Maximum recommended dose: 300 mg/day (150 mg twice daily) for patients with paroxysmal supraventricular arrhythmias 1
• For PAF specifically, increasing from 50 mg to 100 mg twice daily provides substantial efficacy improvement without significantly increasing adverse events 1
• Doses up to 200 mg twice daily may be used in some patients, though this exceeds the typical maximum for PSVT/PAF 2, 1

Efficacy by Dose

The dose-response relationship demonstrates clear benefit with escalation:

• At 50 mg twice daily: approximately 50% of PSVT patients remain arrhythmia-free 3
• At 100 mg twice daily: approximately 70% efficacy for PSVT 3
• At 150 mg twice daily: 86% of PSVT patients and 61% of PAF patients remain arrhythmia-free 3
• Overall success rates in clinical practice: 87% for PSVT and 73% for PAF patients show symptomatic improvement 4

Alternative Dosing Strategies

Pill-in-the-Pocket Approach

• Single oral loading dose: 200-300 mg for acute cardioversion of recent-onset AF 2
• This approach requires prior safety verification in a monitored setting 2
• Conversion typically occurs within 2-4 hours, with success rates of 57-68% at 2-4 hours and 75-91% at 8 hours 2
• In pediatric studies, single doses of approximately 3 mg/kg successfully terminated PSVT in 88% of episodes during follow-up 5

Maintenance Adjustments

• Some patients adequately controlled at 12-hour intervals may require 8-hour dosing intervals for optimal control 1
• Once arrhythmia control is achieved, dose reduction may be attempted to minimize side effects while maintaining efficacy 1

Critical Safety Considerations

Absolute Contraindications

Flecainide must NOT be used in patients with: 2, 1

• Structural heart disease (including ischemic heart disease, abnormal left ventricular function) 2
• Cardiogenic shock 2
• Pre-existing second- or third-degree AV block or sinus node dysfunction (without pacemaker) 2
• Brugada syndrome 2

High-Risk Populations

• Chronic atrial fibrillation patients: Show lowest efficacy (56%) and highest cardiac adverse event rates (29% in one study) 4
• All patients with chronic AF in one study had structural heart disease and experienced more frequent cardiac side effects 4
• Renal impairment: Requires dose adjustment; if creatinine clearance <35 mL/min, reduce initial dose and extend dosing intervals 1

Proarrhythmic Risks

• Atrial flutter with 1:1 AV conduction is a serious risk, potentially causing rapid ventricular rates 2
• This risk necessitates concomitant AV nodal blocking therapy (beta-blocker or calcium channel blocker) when treating atrial flutter 2
• Two cases of atrial fibrillation with rapid ventricular response occurred in clinical trials, one associated with pulmonary edema 6
• Overall proarrhythmic event rate: approximately 2% in PSVT/PAF populations without structural heart disease 4, 6

Monitoring Requirements

During Initiation

• Hospital initiation is NOT required for PSVT/PAF patients without structural heart disease 1
• Outpatient initiation is appropriate for selected patients 2
• ECG monitoring should assess QRS duration (avoid if QRS widens excessively) 2

Ongoing Monitoring

• Assess clinical response after each dose adjustment (minimum 4 days) 1
• Monitor for symptoms of heart failure, particularly in the first few days 1
• Evaluate for visual disturbances, dizziness, and headaches (most common non-cardiac adverse effects, occurring in 64-67% of patients) 4

Comparative Context

When flecainide is ineffective or contraindicated:

• Alternative Class IC agent: Propafenone shows similar efficacy (86% vs 93% for 12-month effective treatment of PSVT) 2
• First-line alternatives: Beta-blockers, diltiazem, or verapamil are recommended before flecainide in patients who prefer medical management over catheter ablation 2
• Catheter ablation: Remains the definitive treatment with >95% success rates for PSVT 2

Special Populations

Pediatric Dosing

• Initial dose: 50 mg/m² body surface area daily (divided into 2-3 doses) for infants <6 months 1
• For children >6 months: 100 mg/m² per day initially, maximum 200 mg/m² per day 1
• Therapeutic plasma levels: 200-500 ng/mL (occasionally up to 800 ng/mL may be required) 1
• Critical warning: Small dose changes can cause disproportionate plasma level increases in children; frequent monitoring is essential 1

Pregnancy

• Limited data exist for flecainide use in pregnancy 2
• When necessary, use the lowest effective dose and avoid first trimester if possible 2