Makindo Medical Notes

⚡ Propafenone hydrochloride is a Class Ic antiarrhythmic used for the suppression of supraventricular and ventricular tachyarrhythmias. It slows cardiac conduction, particularly through the His–Purkinje system and accessory pathways. 💡 Key safety tip: if the QRS interval widens by >20% from baseline, the dose should be reduced or stopped until ECG normalises.

📘 About

• Always check the BNF entry for latest indications, cautions, and monitoring requirements.
• Pharmacologically similar to flecainide but somewhat less potent.
• Possesses mild β-blocking and calcium-channel-blocking activity, which can contribute to bradycardia or bronchospasm in susceptible patients.
• Used under specialist supervision for rhythm control of atrial fibrillation, paroxysmal supraventricular tachycardia (PSVT), and certain ventricular arrhythmias.

⚙️ Mode of Action

• Blocks fast sodium channels in phase 0 of the cardiac action potential → slows conduction velocity and prolongs QRS complex.
• Suppresses re-entry pathways, including those in Wolff–Parkinson–White (WPW) and other accessory tracts.
• Weak non-selective β-blocking activity → caution in asthma/COPD or heart failure.
• Negative inotropic effect may worsen LV dysfunction.

💊 Indications & Doses

• Ventricular arrhythmias: 150 mg three times daily, increased if necessary to a maximum of 300 mg three times daily.
• Supraventricular arrhythmias (including AF/PSVT): specialist-initiated, similar oral dosing range; ECG and plasma level monitoring required during titration.
• Available as immediate-release and modified-release tablets — not interchangeable mg-for-mg.

⚗️ Monitoring

• Baseline and periodic ECGs: check QRS, PR, and QT intervals.
• Stop or reduce dose if QRS widens > 20% or if PR > 200 ms.
• Monitor electrolytes (especially K⁺ and Mg²⁺) and renal/hepatic function.

🔄 Interactions

• See BNF for full details.
• ⚠️ Additive conduction slowing with other antiarrhythmics (e.g. amiodarone, β-blockers, verapamil).
• Inhibits CYP2D6 → may raise levels of metoprolol, desipramine, or certain SSRIs.
• Plasma levels increased by CYP2D6 inhibitors (e.g. fluoxetine, paroxetine, quinidine).

⚠️ Cautions

• Initiate under specialist supervision with ECG monitoring.
• Use with caution in structural heart disease, ischaemic cardiomyopathy, or LV dysfunction due to pro-arrhythmic risk.
• May exacerbate bradycardia or hypotension.
• Caution in hepatic impairment (hepatic metabolism → active metabolites).

🚫 Contraindications

• Severe obstructive pulmonary disease (β-blocking effect).
• Heart block (2°/3°) without pacemaker support.
• Brugada syndrome or history of pro-arrhythmia with Class I agents.
• Cardiogenic shock (unless arrhythmia-induced).
• Severe bradycardia, uncontrolled heart failure.

💥 Adverse Effects

• Cardiac: conduction block, bradycardia, new or worsened arrhythmia, heart failure exacerbation.
• Neurological: dizziness, blurred vision, tremor.
• GI: nausea, metallic taste, constipation.
• Hepatic: transient enzyme elevation or cholestatic jaundice.
• Rare: agranulocytosis, lupus-like reactions.

🧠 Teaching Note

Propafenone is a Class Ic sodium-channel blocker with additional β-blocking effects. It highlights why all Class I agents must be used with care — they can convert a stable rhythm disturbance into a lethal one, particularly in structural heart disease (CAST trial). Always titrate slowly, monitor the ECG, and reassess if QRS widens or symptoms worsen.

📚 References

• BNF: Propafenone
• Resuscitation Council UK — Arrhythmia Management (2023)
• Katzung BG. Basic & Clinical Pharmacology (15th ed.)
• ACC/AHA/HRS Guidelines for the Management of Atrial Fibrillation (2023)