Propafenone: Comprehensive Drug Monograph

Pharmacokinetic Profile

Half-Life

2–10 h (extensive metabolizers, >90% of patients); 10–32 h (poor metabolizers, <10%)

Metabolism

Hepatic — CYP2D6 (major), CYP3A4 and CYP1A2 (minor)

Protein Binding

>95% (concentration range 0.5–2 mcg/mL)

Bioavailability

Dose-dependent: 3.4% (150 mg tablet) to 10.6% (300 mg tablet)

Volume of Distribution

~252 L total; central compartment ~1.1 L/kg

Clinical Information

Drug Class

Class IC antiarrhythmic (Vaughan Williams)

Available Doses

IR tablets: 150, 225 mg
SR capsules: 225, 325, 425 mg

Route

Oral (IV available outside the United States)

Renal Adjustment

No specific reduction; monitor for accumulation

Hepatic Adjustment

Bioavailability rises to ~70% in severe impairment — consider dose reduction or alternative

Pregnancy

PLLR labeling — no clear human signal; use only if benefit justifies risk

Lactation

Present in milk at low levels; consider risk–benefit

Schedule / Status

Prescription, non-controlled

Boxed Warning

Yes — Class IC mortality (CAST class effect)

Generic Available

Yes (IR tablets and SR capsules)

Indications

Indication	Approved Population	Therapy Type	Status
Symptomatic atrial fibrillation (paroxysmal or persistent) — prolong time to recurrence in patients without structural heart disease	Adults	Maintenance of sinus rhythm	FDA Approved (Rythmol SR)
Paroxysmal atrial fibrillation/flutter (PAF) with disabling symptoms — prolong time to recurrence in patients without structural heart disease	Adults	Maintenance of sinus rhythm	FDA Approved (Rythmol IR)
Paroxysmal supraventricular tachycardia (PSVT) with disabling symptoms — prolong time to recurrence in patients without structural heart disease	Adults	Maintenance of sinus rhythm	FDA Approved (Rythmol IR)
Documented life-threatening ventricular arrhythmias (e.g., sustained VT) — initiate treatment in hospital	Adults — when benefits outweigh risks; lesser ventricular arrhythmias not recommended	Monotherapy	FDA Approved (Rythmol IR)
Pill-in-the-pocket cardioversion of recent-onset symptomatic AF	Selected outpatients without structural heart disease, after in-hospital tolerance demonstration	Single-dose self-administration with concomitant AV-nodal blocker	Off-Label (Class IIa, both AHA and ESC)

Propafenone is a Class IC antiarrhythmic positioned in current AF guidelines as a rhythm-control option for patients with no significant structural heart disease — namely no prior myocardial infarction, no clinically meaningful left ventricular hypertrophy, no left ventricular systolic dysfunction, and no obstructive coronary artery disease. The 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline gives antiarrhythmic-drug therapy (including propafenone and flecainide) a Class IIa recommendation for long-term maintenance of sinus rhythm, a downgrade from the previous Class I assignment that reflects the rising role of catheter ablation. The 2024 ESC/EACTS atrial fibrillation guideline similarly identifies propafenone and flecainide as rhythm-control choices in patients without coronary artery disease, severe left-ventricular hypertrophy, or impaired LV systolic function, and stipulates that a beta-blocker or non-dihydropyridine calcium channel blocker be co-prescribed to prevent 1:1 atrial flutter conduction.

Off-label use — evidence summary

Pill-in-the-pocket cardioversion (Alboni et al., NEJM 2004): in 210 selected outpatients with mild or no heart disease, a single oral loading dose of propafenone (600 mg if ≥70 kg, 450 mg if <70 kg) or flecainide successfully terminated 94% of arrhythmic episodes, with a mean time to symptom resolution of approximately 113 minutes. Adverse events occurred in 7% — chiefly non-cardiac, with 1 episode of 1:1 atrial flutter. Evidence quality: moderate.

AVNRT, AVRT and accessory-pathway-mediated tachycardias: propafenone slows accessory-pathway conduction and is an option for chronic suppression. Evidence quality: moderate (small RCTs and registries; supported by 2015 ACC/AHA/HRS SVT guideline).

Atrial flutter: propafenone alone risks 1:1 atrioventricular conduction; an AV-nodal blocker should be co-administered. Evidence quality: low to moderate.

Dose

Dosing

Clinical Scenario	Starting Dose	Maintenance Dose	Maximum Dose	Notes
PAF / PSVT — IR formulation (rhythm maintenance)	150 mg PO q8h (450 mg/day)	225 mg PO q8h (675 mg/day)	300 mg PO q8h (900 mg/day)	Titrate at minimum 3–4 day intervals. Safety of doses >900 mg/day not established. May be taken with or without food
Symptomatic AF — SR formulation (maintenance of sinus rhythm)	225 mg PO q12h	325 mg PO q12h	425 mg PO q12h	Titrate at minimum 5-day intervals. SR is not bioequivalent to IR mg-for-mg. Do not crush, chew, or divide capsules
Documented life-threatening ventricular arrhythmias (IR)	150 mg PO q8h	225–300 mg PO q8h	300 mg PO q8h	Per FDA label, initiate in hospital with continuous ECG monitoring
Pill-in-the-pocket (off-label) recent-onset AF, ≥70 kg	600 mg PO single dose			Tolerance must be established in a monitored setting before outpatient self-administration; concurrent AV-nodal blocker required Do not repeat within 24 hours
Pill-in-the-pocket (off-label) recent-onset AF, <70 kg	450 mg PO single dose			Same monitoring requirements as above

Population-Specific Adjustments

Population	Recommendation	Rationale
Hepatic impairment	Consider dose reduction; titrate slowly with close ECG and clinical monitoring	Bioavailability rises from 3–40% to ~60–70% with severe hepatic dysfunction; mean half-life extends to ~9 h
Renal impairment	No specific dose reduction in the FDA label; monitor for signs of overdose	~50% of metabolites are renally excreted; PK in CKD is incompletely characterized
Significant QRS widening or 2°/3° AV block	Reduce dose	FDA label specifically calls for dose reduction in these conduction findings
Elderly (≥65 y)	Start at the low end; titrate cautiously	Greater frequency of decreased hepatic, renal, or cardiac function and concomitant therapy
CYP2D6 poor metabolizers (~6% of Caucasians)	Same starting dose; titrate cautiously and monitor for exaggerated beta-blockade	Plasma concentrations 1.5–2× higher at therapeutic doses; greater inter-individual variability requires careful ECG-guided titration
Concomitant CYP2D6 + CYP3A4 inhibitor	Avoid combination	FDA label warns against simultaneous use of a CYP2D6 inhibitor and a CYP3A4 inhibitor with propafenone
Pediatric	Safety and effectiveness not established	Off-label use restricted to specialist paediatric electrophysiology

Clinical pearl — initiation strategy

Most experienced electrophysiologists initiate propafenone with a baseline ECG, an ECG within the first 1–2 days of therapy, and a repeat ECG after each titration step. The FDA label specifies that the dose should be reduced in patients who develop significant QRS widening or second- or third-degree AV block. Inpatient telemetry initiation is standard for patients with conduction-system disease, and it is mandatory for those starting therapy for life-threatening ventricular arrhythmia.

SR ↔ IR conversion

The two formulations are not bioequivalent on a mg-for-mg basis. When switching between IR and SR, restart from the manufacturer’s recommended initial dose rather than converting milligram totals. SR capsules must be swallowed whole.

Pharmacology

Mechanism of Action

Propafenone is a Vaughan Williams Class IC antiarrhythmic whose primary action is blockade of the fast inward sodium current in cardiac membranes. It reduces upstroke velocity (phase 0) of the monophasic action potential, an effect most marked in Purkinje fibres and, to a lesser extent, in working myocardium. The drug raises the diastolic excitability threshold, prolongs the effective refractory period, and reduces both spontaneous automaticity and triggered activity. These effects translate clinically into prolongation of the PR interval and widening of the QRS complex; effects on the QT interval are minor once corrected for QRS prolongation. Propafenone exerts modest, non-selective beta-adrenergic blockade — approximately 1/40 the potency of propranolol on a per-milligram basis in humans — which becomes clinically relevant at higher plasma concentrations and in CYP2D6 poor metabolizers. At very high concentrations in vitro, propafenone also inhibits L-type calcium current and several cardiac potassium currents, but these effects are not believed to contribute substantially to its antiarrhythmic action. The principal active metabolite, 5-hydroxypropafenone, has sodium-channel blocking activity comparable to the parent compound but roughly 10-fold less beta-blocking potency.

ADME Profile

Parameter	Value	Clinical Implication
Absorption	Nearly complete oral absorption; peak plasma levels at approximately 3.5 hours. Absolute bioavailability is dose- and formulation-dependent owing to saturable first-pass metabolism: 3.4% for the 150 mg tablet and 10.6% for the 300 mg tablet	Non-linear pharmacokinetics — small dose increases can yield disproportionate rises in plasma concentration. Multiple-dose administration is unaffected by food intake
Distribution	Total volume of distribution ~252 L; central compartment ~88 L (1.1 L/kg). Plasma protein binding >95%, predominantly to α₁-acid glycoprotein	Rapid tissue distribution; high protein binding limits dialysability, so haemodialysis is of little use in overdose
Metabolism	Hepatic metabolism in two genetically determined patterns. Major CYP2D6 pathway (>90% of patients) generates the active 5-hydroxypropafenone. Minor pathways via CYP3A4 and CYP1A2 generate N-depropylpropafenone (norpropafenone, also active). Approximately 6% of Caucasians and lesser proportions in other populations are CYP2D6-deficient slow metabolizers	Strong CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine, ritonavir) phenoconvert extensive metabolizers to slow-metabolizer kinetics, with markedly higher exposure and unmasked beta-blockade. Simultaneous CYP2D6 plus CYP3A4 inhibition should be avoided
Elimination	Hepatic biotransformation followed by urinary excretion of metabolites (~50% of metabolites recovered in urine after IR dosing). Elimination half-life: 2–10 hours in extensive metabolizers; 10–32 hours in slow metabolizers. Steady state is reached in 4–5 days in all patients	Steady-state titration intervals of ≥3–4 days (IR) or ≥5 days (SR) are appropriate. Severe hepatic impairment substantially raises bioavailability and prolongs half-life

Side Effects

Frequencies below are drawn primarily from the FDA prescribing information adverse-reaction tables: 474 subjects with supraventricular tachycardia (Rythmol IR) and 2,127 subjects with ventricular arrhythmia. The Rythmol SR US trial in 523 patients with symptomatic AF is also referenced where available.

≥10% Very Common Adverse Effects

Adverse Effect	Incidence	Clinical Note
Unusual taste (often metallic or bitter)	14%	Hallmark adverse effect and a frequent reason for voluntary discontinuation. Often plateaus over time. Worth pre-warning every patient.
Nausea or vomiting	11%	Patients sometimes find symptoms ease when the dose is taken with food, although food does not affect bioavailability at steady state.

1–10% Common Adverse Effects

Adverse Effect	Incidence	Clinical Note
Dizziness	9%	Most pronounced in the first 1–2 weeks; correlates with peak levels and may signal CYP2D6 poor-metabolizer status.
Constipation	8%	Often dose-related; usually responds to standard fibre and hydration measures.
Headache	6%	Generally mild; rule out hypotension or new bradycardia if persistent.
Fatigue	6%	Partially reflects intrinsic beta-blockade; often dose-related.
Blurred vision	3%	Subjective; rarely warrants discontinuation by itself.
Weakness	3%	Distinguish from heart-failure symptoms.
First-degree AV block (in ventricular arrhythmia trials)	2.5%	Expected ECG effect; investigate further if PR >240 ms or with bifascicular block.
Bradycardia (HR <50 bpm) — IR PSVT trial	2%	Equal to placebo in the SR AF trial; risk rises with concurrent beta-blocker, non-DHP CCB, or sinus-node disease.
Dyspnea	2%	Distinguish from heart-failure exacerbation; consider repeat echo if persistent.
Palpitations	2%	May represent breakthrough arrhythmia or proarrhythmia — assess with ECG.
Wide complex tachycardia	2%	Concerning; warrants discontinuation and electrophysiology assessment.
Tremor	2%	Fine action tremor; more frequent in slow metabolizers.
Anorexia, diarrhoea, ataxia (each)	2%	Generally mild and dose-related.
Bundle branch block / intraventricular conduction delay	~1.1–1.2%	Reported in ventricular-arrhythmia trials; reduce dose and consider discontinuation if progressive.
Positive ANA titer (ventricular arrhythmia trials)	~0.7%	Usually asymptomatic and reversible; consider discontinuation if titers persist or rise.

Serious Serious Adverse Effects (Regardless of Frequency)

Adverse Effect	Estimated Frequency	Typical Onset	Required Action
Proarrhythmia — overall (any new or worsened ventricular arrhythmia)	4.7% across all clinical trials	Most often within first week; later events also reported	Discontinue; admit for telemetry; correct electrolytes; cardiovert if unstable
Sustained VT or VF (component of overall proarrhythmia)	~4% in pooled trials; 1.9% in PSVT trial	Often within 14 days of initiation	Stop drug; ACLS as needed; do not rechallenge
New or worsened heart failure (overall trials)	3.7% in ventricular arrhythmia trials (1.9% in PAF/PSVT, 1.0% on Rythmol SR vs 0.8% placebo in AF trial)	Weeks to months	Discontinue; initiate or escalate guideline-directed HF therapy
Second- or third-degree AV block	0.6% / 0.2% respectively (ventricular arrhythmia trials)	First days of therapy or after dose increase	Discontinue; pacing if symptomatic; permanent pacemaker if recurrent
1:1 atrial flutter conduction (paradoxical ventricular acceleration)	~1%	Hours to days after initiation	Co-administer an AV-nodal blocker (beta-blocker or non-DHP CCB) for any flutter-prone patient; cardioversion if unstable
Brugada-pattern ECG unmasking	Rare (postmarketing reports; FDA-listed contraindication once identified)	Within hours to days of first dose	Discontinue immediately; electrophysiology referral; family screening
Bronchospasm in patients with reactive airways	Rare (FDA contraindication for bronchospastic disease)	Minutes to hours	Discontinue permanently; bronchodilator/steroid therapy as needed
Hepatotoxicity (cholestatic, hepatocellular, or mixed; rare fulminant cases)	Rare (postmarketing)	First 1–3 months	Discontinue; hepatology consultation; serial LFTs until normalization
Agranulocytosis or granulocytopenia	Rare	Usually within first 2 months; counts normalize within ~14 days of stopping	Discontinue; CBC; haematology referral
Drug-induced lupus erythematosus	Very rare (single published case with positive rechallenge)	Months to years	Discontinue; usually reversible
Exacerbation of myasthenia gravis	Rare	Variable	Discontinue; specialist input
Hyponatraemia / SIADH, kidney failure, apnea, coma, seizures	Very rare (postmarketing case reports)	Variable	Discontinue; condition-specific management

Discontinuation Discontinuation Rates Due to Adverse Effects

Adults — Rythmol IR (overall)

~20% FDA PI: discontinued for adverse reactions

Top reasons (PSVT trial): nausea/vomiting, dizziness, fatigue, unusual taste, wide complex tachycardia, weakness.

Pediatric

Not established FDA: safety/efficacy not established

Use restricted to specialist paediatric electrophysiology; no labeled dose.

Reason for Discontinuation (PSVT trial, n = 474)	Incidence	Context
Nausea or vomiting	2.9%	Most common GI cause of discontinuation.
Wide complex tachycardia	1.9%	A red-flag finding — non-negotiable trigger to stop and reassess.
Dizziness	1.7%	Often peaks early; consider dose reduction before stopping.
Fatigue	1.5%	Partly reflects intrinsic beta-blockade.
Unusual taste	1.3%	Most common driver of long-term voluntary discontinuation outside trials.
Weakness	1.3%	Often dose-related.
Dyspnea	1.0%	Distinguish from heart failure.
Headache, blurred vision, CHF, others	≤1% each	CHF mandates permanent discontinuation.

Managing the highest-impact toxicity — proarrhythmia

Proarrhythmia is the single most important safety concern with propafenone. In FDA-pooled trials (which included subjects with ventricular arrhythmia, AF/flutter, and PSVT), 4.7% of all subjects had a new or worsened ventricular arrhythmia possibly representing proarrhythmia. The risk was concentrated in patients with structural heart disease: among those with worsening of VT, 92% had a history of VT or VT/VF, 71% had coronary artery disease, and 68% had a prior myocardial infarction. Risk markers include any structural heart disease, QRS widening, electrolyte derangement (K⁺, Mg²⁺), and concurrent QT-prolonging or bradycardic agents. New sustained ventricular arrhythmia, syncope, or marked QRS widening on therapy should prompt immediate discontinuation, electrolyte correction, and continuous monitoring. Rechallenge is generally inadvisable.

Int

Drug Interactions

Propafenone is a substrate of CYP2D6 (major), CYP3A4, and CYP1A2, and is itself an inhibitor of CYP2D6 and a P-glycoprotein inhibitor. The FDA prescribing information specifically warns against simultaneous use of a CYP2D6 inhibitor and a CYP3A4 inhibitor, as the combination may produce hazardous increases in propafenone exposure. The following interactions reflect data from the FDA label, with cross-reference to clinical drug-interaction databases for severity grading.

Major Digoxin

MechanismP-gp inhibition by propafenone reduces digoxin clearance.

EffectSteady-state digoxin AUC rises 60–270%; clearance falls 31–67%.

ManagementReduce digoxin dose at initiation; monitor digoxin levels and titrate to therapeutic range.

FDA PI

Major Warfarin

MechanismInhibition of warfarin metabolism.

EffectWarfarin steady-state plasma concentrations rise ~39%; PT/INR may climb meaningfully in patients on therapy.

ManagementCheck INR within 5–7 days of starting, stopping, or adjusting propafenone; adjust warfarin dose accordingly.

FDA PI

Major Quinidine

MechanismComplete inhibition of CYP2D6, phenoconverting all patients to slow metabolizers.

EffectQuinidine 50 mg TID with propafenone reduces propafenone clearance by 60% and more than doubles steady-state levels; 100 mg quinidine triples propafenone concentrations.

ManagementAvoid concomitant use; co-administration of two Class I antiarrhythmics increases proarrhythmia risk substantially.

FDA PI

Major Amiodarone

MechanismAdditive sodium- and potassium-channel effects with CYP-mediated interaction.

EffectAffects conduction and repolarization; risk of QRS/QT prolongation and bradyarrhythmia.

ManagementFDA: not recommended. Withhold Class IA or III antiarrhythmics for ≥5 half-lives prior to propafenone.

FDA PI

Major Ritonavir

MechanismStrong inhibition of both CYP2D6 and CYP3A4.

EffectSubstantial rise in propafenone exposure with risk of arrhythmia and conduction block.

ManagementFDA: avoid simultaneous use of any CYP2D6 inhibitor and CYP3A4 inhibitor with propafenone; ritonavir falls into both categories. Choose alternative therapy.

FDA PI

Major CYP2D6 inhibitors (paroxetine, fluoxetine, desipramine, sertraline, bupropion)

MechanismCYP2D6 inhibition phenoconverts extensive to slow metabolizer kinetics.

EffectFluoxetine specifically increases S-propafenone AUC by ~50% and R-propafenone AUC by ~50%; unmasks beta-blockade.

ManagementUse the lowest effective propafenone dose; avoid combinations that also include a CYP3A4 inhibitor.

FDA PI

Major Beta-blockers (propranolol, metoprolol)

MechanismCYP2D6 inhibition raises lipophilic beta-blocker levels; additive negative inotropy/chronotropy.

EffectPropranolol steady-state levels rise ~113%; metoprolol levels rise 100–400% (per FDA label).

ManagementMonitor for excess bradycardia, hypotension, fatigue; reduce beta-blocker dose. The FDA label notes that in IR clinical trials, concurrent beta-blocker use did not increase adverse-event rates.

FDA PI

Major Orlistat

MechanismOrlistat reduces propafenone absorption; abrupt cessation removes this effect, producing a surge in plasma levels.

EffectPostmarketing reports of convulsions, AV block, and acute circulatory failure on abrupt orlistat withdrawal in patients stabilised on propafenone.

ManagementAvoid concurrent use; if unavoidable, taper orlistat under monitoring.

FDA PI (postmarketing)

Major QT-prolonging agents (some phenothiazines, TCAs, oral macrolides)

MechanismAdditive repolarization effect; QT interpretation is complicated by QRS widening from propafenone.

EffectIncreased risk of torsades and other ventricular arrhythmias.

ManagementAvoid combination where possible; monitor ECG and electrolytes if used.

FDA PI

Moderate Rifampin

MechanismPotent CYP3A4 induction.

EffectPropafenone plasma concentrations fall ~67% in extensive metabolizers and ~50% in slow metabolizers; antiarrhythmic effect may be lost.

ManagementAvoid; if unavoidable, monitor for arrhythmia recurrence and consider alternative therapy.

FDA PI

Moderate Cimetidine

MechanismMild CYP-mediated inhibition.

Effect~20% increase in steady-state propafenone concentrations.

ManagementSwitch to famotidine or a PPI for acid suppression.

FDA PI

Moderate Verapamil, diltiazem

MechanismAdditive AV-nodal slowing and negative inotropy.

EffectBradycardia, hypotension, AV block, worsening HF.

ManagementCombination is sometimes desirable for AF rate control; start low and monitor ECG and BP closely.

Lexicomp

Moderate Lidocaine (systemic)

MechanismNo significant pharmacokinetic interaction; pharmacodynamic potentiation of CNS effects.

EffectIncreased risk of central nervous system adverse effects of lidocaine.

ManagementUse cautiously; consider lower lidocaine dose if essential.

FDA PI

Moderate Ketoconazole, erythromycin, saquinavir, grapefruit juice

MechanismCYP3A4 inhibition.

EffectIncreased propafenone exposure; clinically meaningful especially in patients who are also on a CYP2D6 inhibitor or are CYP2D6 PMs.

ManagementAvoid combination with simultaneous CYP2D6 inhibition; otherwise monitor closely.

FDA PI

Mon

Monitoring

12-lead ECG Baseline, after initiation, after each titration step, and periodically thereafter
Routine Track PR, QRS, and QT/QTc. The FDA label specifies dose reduction for significant QRS widening or for second- or third-degree AV block. The FDA-reported mean QRS prolongation at 900 mg/day is approximately 17%, and PR prolongation approximately 22%.
Heart rate & BP Each visit; daily during titration
Routine Watch for resting HR <50 bpm or symptomatic hypotension, particularly when combined with beta-blockers or non-DHP calcium-channel blockers.
Echocardiogram Before initiation; repeat for HF symptoms
Routine Document LV ejection fraction and exclude clinically meaningful LVH or valvular disease. Class IC agents are contraindicated in heart failure and in patients with structural heart disease.
Coronary disease assessment Before initiation in patients with risk factors for CAD
Routine CAST-era data identify ischaemic substrate as a major proarrhythmia risk. Both the 2023 ACC/AHA and 2024 ESC AF guidelines exclude propafenone in patients with significant CAD.
Electrolytes (K⁺, Mg²⁺) Baseline and with diuretic changes
Routine Marked electrolyte imbalance is an FDA contraindication. Hypokalaemia and hypomagnesaemia amplify proarrhythmia risk.
Pacemaker function During and after therapy in pacemaker-dependent patients
Trigger-based Propafenone may alter pacing and sensing thresholds; reprogram the device as needed.
Liver function tests Baseline; repeat for symptoms
Trigger-based Idiosyncratic hepatotoxicity (cholestatic, hepatocellular, or fulminant) is rare but reported in postmarketing experience; check ALT/AST/ALP/bilirubin if jaundice, fatigue, or abdominal pain occurs.
Complete blood count If signs of infection or unexplained fever, particularly in the first 3 months
Trigger-based Per the FDA label, agranulocytosis typically occurs within the first 2 months and white-cell counts normalize within ~14 days of stopping the drug.
ANA titer If new arthralgia, rash, or constitutional symptoms
Trigger-based Positive ANA was reported in ~0.7% of subjects; titres are often reversible on discontinuation. Persistent rises warrant consideration of stopping the drug.
Symptoms (palpitations, syncope, dyspnea) Each visit; ad-hoc patient-reported
Routine New syncope or sustained palpitations on therapy must trigger urgent evaluation for proarrhythmia.

Contraindications & Cautions

FDA Boxed Warning — Mortality Class IC mortality signal — extended from CAST

Per the FDA boxed warning, the Cardiac Arrhythmia Suppression Trial (CAST) demonstrated an increased rate of death or reversed cardiac arrest (7.7% vs 3.0% on placebo) in patients with asymptomatic non-life-threatening ventricular arrhythmias following remote myocardial infarction (6 days to 2 years post-MI) treated with the Class IC agents encainide or flecainide.

The applicability of the CAST findings to other populations and to other Class IC agents (including propafenone) is uncertain, but the FDA label states it is prudent to consider any Class IC antiarrhythmic to carry a significant proarrhythmic risk in patients with structural heart disease. Antiarrhythmic agents should generally be avoided in patients with non-life-threatening ventricular arrhythmias even if symptomatic.

Absolute Contraindications (per FDA label)

Heart failure.
Cardiogenic shock.
Sinoatrial, atrioventricular, and intraventricular disorders of impulse generation or conduction (e.g., sick sinus syndrome, AV block) in the absence of an artificial pacemaker.
Known Brugada syndrome.
Bradycardia.
Marked hypotension.
Bronchospastic disorders or severe obstructive pulmonary disease (asthma, severe COPD).
Marked electrolyte imbalance.

Relative Contraindications (Specialist Input Recommended)

Documented or strongly suspected coronary artery disease — CAST-class concern; both 2023 ACC/AHA and 2024 ESC AF guidelines exclude propafenone in patients with CAD.
Significant left-ventricular hypertrophy or LV systolic dysfunction — guideline-defined exclusion criteria for Class IC therapy.
Pacemaker dependence — propafenone may alter pacing and sensing thresholds.
Concurrent use of any antiarrhythmic that prolongs the QT interval — the FDA label advises avoidance with Class IA and III antiarrhythmics, with a 5-half-life washout period when transitioning.
Simultaneous CYP2D6 + CYP3A4 inhibitors — the FDA label specifically advises against this combination.
Significant hepatic impairment — bioavailability rises markedly; consider alternative therapy or careful dose reduction.
Pregnancy — limited data; use only if benefits outweigh risks. Continuous fetal/neonatal monitoring recommended during therapy and around delivery.

Use with Caution

Older adults — heightened sensitivity to bradyarrhythmia, falls, and orthostatic effects; FDA recommends starting at the low end of the dosing range.
Renal impairment — limited PK data; monitor for signs of accumulation.
Concurrent beta-blocker, non-DHP CCB, or digoxin use — additive AV-nodal slowing; dose adjustments often required.
CYP2D6 poor-metabolizer status — exposure is 1.5–2× higher at therapeutic doses; titrate slowly.
Lactation — drug and metabolite present in milk at low levels; balance maternal benefit against potential infant exposure.
Myasthenia gravis — exacerbations have been reported.

Patient Counselling

Purpose of Therapy

Frame propafenone as a maintenance therapy whose role is to keep the heart in normal rhythm and reduce episodes of irregular heartbeats such as atrial fibrillation or supraventricular tachycardia. Patients should understand that the drug suppresses arrhythmia rather than curing it; missed doses or abrupt discontinuation may allow the arrhythmia to return. Effectiveness is gauged through symptom diaries, periodic ECGs, and ambulatory rhythm monitoring when appropriate.

How to Take

Immediate-release propafenone is taken every 8 hours; sustained-release every 12 hours. The two formulations are not interchangeable, and SR capsules must be swallowed whole — never crushed, chewed, or split. Doses may be taken with or without food, but consistent timing helps minimize taste disturbance and nausea. A missed dose should be taken as soon as remembered unless the next dose is due within a couple of hours, in which case the missed dose is skipped — patients should never double up. Patients travelling across time zones should agree a brief plan with their prescriber to avoid unintentional dose stacking or gaps.

Unusual or metallic taste

Tell patient This is the most common side effect (about 1 in 7 patients) and is not dangerous. It often plateaus over weeks. Sugar-free mints, gum, or rinsing the mouth after each dose may help. Taking with food can also blunt the taste.

Call prescriber If the taste change makes you stop eating, lose weight, or you can no longer tolerate the medication.

Dizziness, fatigue, or weakness

Tell patient These are most prominent in the first 1–2 weeks and usually improve. Stand up slowly, hydrate well, and avoid alcohol while you adjust. Do not drive until you know how the medication affects you.

Call prescriber If you faint, fall, develop chest pain, or your heart rate drops below 50 beats per minute. Persistent dizziness beyond 2–3 weeks also deserves a call.

Palpitations or returning irregular heartbeat

Tell patient Some breakthrough episodes are expected as the dose is being optimized. Keep a brief log: date, time, duration, and symptoms.

Call prescriber If palpitations are sustained more than 30 minutes, are accompanied by chest pain, severe shortness of breath, or fainting, or are markedly different from previous episodes — seek emergency care for fainting.

New or worsening shortness of breath, leg swelling

Tell patient Propafenone can occasionally weaken the heart’s pumping function. Notice changes in your ability to climb stairs, lie flat, or fit into your usual shoes.

Call prescriber If you gain more than 2 kg in a week, develop new ankle swelling, wake up short of breath, or cannot complete previously routine activities.

Bruising or bleeding (warfarin users)

Tell patient Propafenone can raise warfarin levels by about 40%. Expect an INR check within 1 week of starting, stopping, or changing the propafenone dose.

Call prescriber For unusual bruising, blood in urine or stool, prolonged bleeding from cuts, or any major bleed.

Yellowing of skin or eyes, dark urine, abdominal pain

Tell patient These can be signs of a rare liver reaction. They usually resolve when the medication is stopped.

Call prescriber Promptly. Do not stop the drug on your own, but seek same-day evaluation.

Sore throat, fever, unusual infection

Tell patient Very rarely, propafenone can lower white blood cell counts, particularly in the first 2 months. Most fevers are not from the medication, but they are worth a quick call.

Call prescriber For fever >38.5 °C, mouth ulcers, or recurrent infections — a quick blood count is reassuring.

New medications, supplements, or grapefruit juice

Tell patient Many common drugs interact with propafenone — including some antidepressants (paroxetine, fluoxetine), some antibiotics, antifungals, HIV medications, and certain heart medications. Always check before starting anything new, including over-the-counter cough or cold remedies.

Call prescriber Before starting any new prescription, herbal product, or supplement. A brief pharmacy review is worthwhile.

Stopping the medication

Tell patient Do not stop propafenone suddenly without medical advice — your previous arrhythmia may return. If you are also on orlistat for weight loss, stopping orlistat suddenly while still taking propafenone has caused serious side effects, so the change should always be supervised.

Call prescriber Before stopping or making any change in either medication.

Ref

Sources

Regulatory (Prescribing Information)

U.S. Food and Drug Administration. RYTHMOL (propafenone hydrochloride) tablets — Prescribing Information. Revised November 2018. accessdata.fda.gov Primary source for IR formulation indications, dosing (150 mg q8h start, max 300 mg q8h), boxed mortality warning, contraindications, and adverse reaction frequencies.
U.S. Food and Drug Administration. RYTHMOL SR (propafenone hydrochloride extended-release capsules) — Prescribing Information. Revised February 2013. accessdata.fda.gov Primary source for SR formulation: AF maintenance indication, 225/325/425 mg q12h dosing, and the U.S. RAFT trial reference.
European Medicines Agency / national regulators. Rytmonorm (propafenone) Summary of Product Characteristics. medicines.org.uk European prescribing reference, including IV formulation data not currently available in the United States.

Key Clinical Trials

Pritchett ELC, Page RL, Carlson M, et al. Efficacy and safety of sustained-release propafenone (propafenone SR) for patients with atrial fibrillation. Am J Cardiol. 2003;92(8):941–946. doi.org/10.1016/S0002-9149(03)00974-3 Pivotal RAFT trial supporting SR approval; demonstrated dose-related prolongation of time to AF recurrence.
Alboni P, Botto GL, Baldi N, et al. Outpatient treatment of recent-onset atrial fibrillation with the “pill-in-the-pocket” approach. N Engl J Med. 2004;351(23):2384–2391. doi.org/10.1056/NEJMoa041233 Landmark trial establishing safety and efficacy of self-administered single-dose propafenone (600 mg ≥70 kg, 450 mg <70 kg) for AF cardioversion outside hospital.
Echt DS, Liebson PR, Mitchell LB, et al. Mortality and morbidity in patients receiving encainide, flecainide, or placebo: the Cardiac Arrhythmia Suppression Trial. N Engl J Med. 1991;324(12):781–788. doi.org/10.1056/NEJM199103213241201 CAST publication that defined the class-wide proarrhythmia mortality concern subsequently extended to all Class IC agents including propafenone.
Stroobandt R, Stiels B, Hoebrechts R. Propafenone for conversion and prophylaxis of atrial fibrillation. Propafenone Atrial Fibrillation Trial Investigators. Am J Cardiol. 1997;79(4):418–423. doi.org/10.1016/S0002-9149(96)00779-5 Multicentre trial supporting use of propafenone for both acute conversion and chronic suppression of paroxysmal AF.

Guidelines

Joglar JA, Chung MK, Armbruster AL, et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation. J Am Coll Cardiol. 2024;83(1):109–279. doi.org/10.1016/j.jacc.2023.08.017 Current US AF guideline. Class IIa recommendation for antiarrhythmic-drug therapy (including propafenone) for sinus rhythm maintenance in patients without structural heart disease.
Van Gelder IC, Rienstra M, Bunting KV, et al. 2024 ESC Guidelines for the management of atrial fibrillation developed in collaboration with the EACTS. Eur Heart J. 2024;45(36):3314–3414. doi.org/10.1093/eurheartj/ehae176 Current European AF guideline; recommends propafenone or flecainide for long-term rhythm control in patients without CAD, severe LVH, or LV systolic dysfunction, with concurrent AV-nodal blocker.
Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. Circulation. 2016;133(14):e506–e574. doi.org/10.1161/CIR.0000000000000311 Reference for propafenone’s role in PSVT, AVNRT, and accessory-pathway-mediated tachycardias.

Mechanistic / Basic Science

Funck-Brentano C, Kroemer HK, Lee JT, Roden DM. Propafenone. N Engl J Med. 1990;322(8):518–525. doi.org/10.1056/NEJM199002223220806 Classic review of mechanism of action, electrophysiology, and CYP2D6 polymorphism effects on propafenone.
Siddoway LA, Thompson KA, McAllister CB, et al. Polymorphism of propafenone metabolism and disposition in man: clinical and pharmacokinetic consequences. Circulation. 1987;75(4):785–791. doi.org/10.1161/01.CIR.75.4.785 Defined the EM/PM CYP2D6 phenotypes for propafenone and their consequences for beta-blockade and dosing.

Pharmacokinetics / Special Populations

Bryson HM, Palmer KJ, Langtry HD, Fitton A. Propafenone. A reappraisal of its pharmacology, pharmacokinetics and therapeutic use in cardiac arrhythmias. Drugs. 1993;45(1):85–130. doi.org/10.2165/00003495-199345010-00008 Comprehensive PK/PD review covering bioavailability non-linearity, metabolism, and special populations.
Lee JT, Kroemer HK, Silberstein DJ, et al. The role of genetically determined polymorphic drug metabolism in the beta-blockade produced by propafenone. N Engl J Med. 1990;322(25):1764–1768. doi.org/10.1056/NEJM199006213222502 Demonstrated that the beta-blocking effects of propafenone are far more pronounced in CYP2D6 poor metabolizers.
Reiffel JA, Capucci A. “Pill in the Pocket” antiarrhythmic drugs for orally administered pharmacologic cardioversion of atrial fibrillation. Am J Cardiol. 2021;140:55–61. doi.org/10.1016/j.amjcard.2020.10.063 Updated review of the pill-in-the-pocket strategy with practical patient-selection and dosing considerations.