Makindo Medical Notes

Note: Disopyramide is a Class Ia antiarrhythmic. Its use in the UK is rare and generally limited to specialist cardiology practice (e.g. hypertrophic cardiomyopathy). Always prescribe with ECG monitoring and consult the BNF or specialist guidance.

📖 About

• Class Ia antiarrhythmic (sodium channel blocker with moderate conduction slowing).
• Also has anticholinergic properties and a negative inotropic effect.
• Prolongs the QT interval and action potential duration (torsades risk).
• Now rarely used outside specialist practice.

⚙️ Mode of Action

• Fast Na⁺ channel blockade: ↓ phase 0 depolarisation in cardiac myocytes.
• Prolongs repolarisation → ↑ QT interval.
• Negative inotropy and anticholinergic effects (reduce LV outflow tract obstruction in HCM).
• ~90% protein bound; metabolised hepatically (CYP3A4).

🩺 Indications

• Hypertrophic cardiomyopathy (HCM) with LV outflow tract obstruction, especially when β-blockers or verapamil are insufficient.
• Ventricular tachycardia (post-MI): historical use, but not first-line today.
• Other ventricular arrhythmias only under specialist guidance.

🚫 Contraindications

• Pre-existing QT prolongation or torsades de pointes.
• Severe LV systolic dysfunction or overt heart failure.
• 2nd/3rd-degree AV block or sick sinus syndrome (unless paced).
• Glaucoma, urinary retention, myasthenia gravis (anticholinergic effects).
• Pregnancy: avoid unless essential, seek specialist advice.

💊 Dosing – Disopyramide (BNF; specialist use only)

❗ Side Effects

• Cardiac: QT prolongation, torsades de pointes, AV block, bradycardia, worsening heart failure.
• Anticholinergic: Dry mouth, constipation, urinary retention, blurred vision, worsening of glaucoma.
• Metabolic: Hypoglycaemia (rare, but important in frail/elderly).
• Other: rash, fatigue, dizziness.

🔄 Interactions

• QT-prolonging drugs: Additive risk (amiodarone, quinidine, sotalol, macrolides, fluoroquinolones, antipsychotics).
• CYP3A4 inhibitors: Macrolides, azole antifungals ↑ disopyramide levels/toxicity.
• Negative inotropes: β-blockers, verapamil, diltiazem ↑ risk of bradycardia and LV dysfunction.
• Avoid concurrent strong anticholinergics (urinary retention, glaucoma exacerbation).

📚 References

• BNF: Disopyramide
• Summary of Product Characteristics
• ESC Guidelines on Ventricular Arrhythmias (2022)