Adult: For rapid control or short-term prophylaxis of ventricular tachyarrhythmias, AV nodal reciprocating tachycardia, arrhythmias associated with Wolff-Parkinson-White syndrome, paroxysmal atrial fibrillation/flutter associated with disabling symptoms: Acute or emergency cases: 2 mg/kg via inj over at least 10 minutes. Max: 150 mg. Administer initial dose in patients with history of heart failure over 30 minutes, stop inj when arrhythmia is controlled. Prolonged therapy: Initially, 2 mg/kg up to Max of 150 mg via slow inj over 30 minutes; followed by a continuous infusion of 1.5 mg/kg/hour over the 1st hour, then 0.1-0.25 mg/kg/hour thereafter. Max cumulative dose: 600 mg in 24 hours. Infusion beyond 24 hours is not recommended. Switch to oral therapy as soon as possible. Continuous ECG monitoring is required throughout administration.
Oral Supraventricular arrhythmias
Adult: As prophylaxis for paroxysmal supraventricular tachycardias including AV nodal re-entrant tachycardia, AV re-entrant tachycardia, and other disabling supraventricular tachycardias of unspecified mechanism associated with disabling symptoms, and paroxysmal atrial fibrillation/flutter associated with disabling symptoms in patients without structural heart disease: As conventional tab: Initially, 50 mg 12 hourly; may be increased in increments of 50 mg bid at 4-day intervals until efficacy is obtained. Max: 300 mg daily. As controlled-release cap: 100 mg once daily; may be increased gradually in increments of 100 mg at intervals of at least 7 days, according to response and tolerability. Max: 300 mg daily. Dosage and treatment recommendations may vary among countries and between individual products (refer to specific product guidelines).
Oral Ventricular arrhythmias
Adult: As prophylaxis for life-threatening cases such as sustained ventricular tachycardia in patients without structural heart disease: As conventional tab: Initially, 50-100 mg 12 hourly; may increase in increments of 50 mg bid at 4-day intervals until efficacy is obtained. Max: 400 mg daily. Dose frequency may be adjusted to 8 hourly for patients who are intolerant and inadequately controlled by the 12-hour dose interval. Consider reducing the dose once adequate response is achieved. As controlled-release cap: 100 mg once daily; may be increased gradually in increments of 100 mg at intervals of at least 7 days, according to response and tolerability. Max: 300 mg daily. Dosage and treatment recommendations may vary among countries and between individual products (refer to specific product guidelines).
What are the brands available for Flecainide in Thailand?
Patients taking amiodarone: Reduce dose of flecainide to 50%. Close monitoring of any side effects and plasma levels is recommended.
Pharmacogenomics:
Flecainide is a drug with a narrow therapeutic index. Its metabolism is mediated by CYP2D6 isoenzyme, forming inactive metabolites.
Individuals with reduced CYP2D6 activity, classified as poor or intermediate metabolisers, exhibit significantly elevated plasma concentrations of flecainide. There is limited evidence involving the clinical consequences of the gene-drug interaction; however, certain action is recommended given flecainide's narrow therapeutic range. Pre-emptive genotyping before treatment initiation may be beneficial to prevent side effects and assess drug effectiveness.
Royal Dutch Pharmacists Association - Pharmacogenetics Working Group (DPWG) Guideline as of November 2018:
Genotype
Implications
Recommendations
CYP2D6 ultrarapid metabolisers
Individuals carrying a gene duplication in the absence of inactive allele (e.g. *3‐*8, *11‐*16, *19‐*21, *38, *40, *42) or allele with decreased activity (e.g. *9, *10, *17, *29, *36, *41).
Increased metabolism of flecainide to inactive metabolites which may indicate a higher dose requirement.
Monitor plasma levels and ECG to guide treatment or selecting alternative antiarrhythmic agents that are not metabolised by CYP2D6 (e.g. sotalol, disopyramide, quinidine, amiodarone).
CYP2D6 intermediate metabolisers
Individuals carrying 2 alleles with decreased activity (e.g. *9, *10, *17, *29, *36, *41), 1 active allele (e.g. *1, *2, *33, *35) and 1 inactive allele (e.g. *3‐*8, *11‐*16, *19‐*21, *38, *40, *42), or 1 allele with decreased activity (e.g. *9, *10, *17, *29, *36, *41) and 1 inactive allele (e.g. *3‐*8, *11‐*16, *19‐*21, *38, *40, *42).
Decreased metabolism of flecainide to inactive metabolites which may increase risk of adverse effects.
Reduce dose by 75% of the standard dose for indications other than Brugada syndrome. Closely monitor ECG and plasma concentration.
Decreased metabolism to inactive metabolites which increases risk of adverse effects.
Reduce dose by 50% of the standard dose. Closely monitor ECG and plasma concentration.
Renal Impairment
Oral:
CrCl (mL/min/1.73 m2)
Dosage
≤35
As conventional tab: Max initial dose: 100 mg daily or 50 mg bid. Dose may be adjusted very cautiously according to serum trough concentration and clinical response.
Intravenous:
CrCl (mL/min/1.73 m2)
Dosage
≤35
Reduce dose by 50%. Frequent monitoring of plasma level is recommended. Switch to oral therapy as soon as possible.
Hepatic Impairment
Oral:
Dose adjustment may be necessary. Frequent monitoring of plasma levels is required.
Administration
Flecainide May be taken with or without food.
Reconstitution
IV: Dilute with 20 mL of dextrose 5% solution or with ≥500 mL of NaCl or Lactated Ringer's solution.
Incompatibility
IV: Dilution with <500 mL of alkaline solutions or chloride-containing solutions (e.g. NaCl 0.9%, Lactated Ringer's solution) may cause precipitation.
Contraindications
Structural heart disease, pre-existing 2nd- or 3rd-degree AV block, right bundle branch block associated with left hemiblock, atrial conduction defects, and sinus node dysfunction in the absence of a functioning pacemaker; abnormal left ventricular function, cardiogenic shock, heart failure, history of MI with asymptomatic non-sustained ventricular tachycardia and/or asymptomatic ventricular contractions; long-standing atrial fibrillation (without attempt to convert to sinus rhythm); haemodynamically significant valvular heart disease.
Special Precautions
Patient with permanent pacemakers or temporary pacing wires, acute onset of atrial fibrillation following cardiac surgery, predisposition to heart failure. Not indicated for use in patients with chronic atrial fibrillation. Treatment initiation should be in a hospital setting or under direct supervision of physicians. Correction of electrolyte imbalances (e.g. hypokalaemia, hyperkalaemia, hypomagnesaemia) is recommended prior to treatment initiation. CYP2D6 polymorphisms. Severe renal (CrCl ≤35 mL/min) and significant hepatic impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Increased endocardial pacing thresholds and suppress ventricular escape rhythms, 1:1 AV conduction following initial atrial slowing leading to ventricular acceleration; demasking of preexisting Brugada syndrome. Rarely, pulmonary fibrosis, interstitial lung disease, pneumonitis; blood dyscrasias (e.g. thrombocytopenia, leukopenia, granulocytopenia); corneal deposits. Cardiac disorders: Chest pain, palpitations. Eye disorders: Visual disturbances, blurred vision, double vision. Gastrointestinal disorders: Nausea vomiting, constipation, diarrhoea, abdominal pain, dyspepsia, flatulence. General disorders and administration site conditions: Asthenia, fatigue, pyrexia, oedema. Hepatobiliary disorders: Jaundice, elevated liver enzymes. Metabolism and nutrition disorders: Decreased appetite, anorexia. Nervous system disorders: Headache, dizziness, lightheadedness, tremor, nervousness, paraesthesia. Respiratory, thoracic and mediastinal disorders: Dyspnoea. Skin and subcutaneous tissue disorders: Rash. Potentially Fatal: Proarrhythmic effects (e.g. ventricular premature contractions, ventricular fibrillation, ventricular tachycardia); exacerbation of proarrhythmic events and increase risk of mortality in patients with structural heart disease.
This drug may cause dizziness and visual disturbances, if affected, do not drive or operate machinery.
Monitoring Parameters
Monitor ECG, BP, heart rate, periodic serum trough levels (particularly to those with hepatic or renal impairment). Consider pre-emptive genotyping before treatment initiation.
Overdosage
Symptoms: Nausea, vomiting, convulsions, hypotension, bradycardia, widening of QRS complex, PR and QT intervals, ventricular tachycardia, AV nodal block, bundle branch block, asystole, cardiac failure, cardiac arrest, and respiratory failure. Management: Symptomatic and supportive treatment. Perform gastric decontamination of unabsorbed drugs. Administer IV cardiac stimulants or inotropic agents (e.g. dopamine, dobutamine, isoproterenol). May perform mechanical ventilation and circulatory assistance (e.g. intra-aortic balloon pumping) or temporary insertion of transvenous pacemaker in the event of conduction block. These treatments may need to continue for an extended period of time. Forced diuresis with urine acidification may enhance drug elimination.
Drug Interactions
Increased incidence of cardiac arrhythmias or additive effects with other antiarrhythmic or arrhythmogenic drugs. Additive negative inotropic effects with verapamil and β-blockers. May increase the plasma level of digoxin. Potentially Fatal: Increased plasma concentration with CYP2D6 inhibitors such as amiodarone, quinidine, cimetidine, antivirals (e.g. ritonavir, lopinavir, indinavir), neuroleptics, and antidepressants (e.g. paroxetine, fluoxetine).
Action
Description: Mechanism of Action: Flecainide is a Class Ic antiarrhythmic agent with local anaesthetic properties and moderate negative inotropic effects. It alters the transport of ions across cell membranes which slows intracardiac conduction throughout the heart, predominantly in the His-Purkinje system (H-V conduction). Flecainide also reduces the rate of rise of the action potential, slightly prolongs the refractory period, and increases the threshold for electrical stimulation of ventricles. Pharmacokinetics: Absorption: Almost completely absorbed in the gastrointestinal tract. Milk may reduce the absorption in paediatric patients. Bioavailability: Approx 85-90%. Time to peak plasma concentration: Approx 3 hours (range: 1-6 hours). Distribution: Crosses the placenta and enters breast milk. Plasma protein binding: Approx 40%. Metabolism: Extensively metabolised by CYP2D6 isoenzyme into m-O-dealkylated flecainide and m-O-dealkylated lactam of flecainide (major metabolites). Excretion: Mainly via urine (30% [range: 10-50%] as unchanged drug; remainder as metabolites); faeces (5%). Elimination half-life: Approx 20 hours (range: 12-27 hours).
Chemical Structure
Flecainide Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 3356, Flecainide. https://pubchem.ncbi.nlm.nih.gov/compound/Flecainide. Accessed June 26, 2025.
Storage
Tab: Store between 15-30°C. Intact vial: Store below 30°C. Do not freeze. Protect from light.
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