Makindo Medical Notes

Note: Disopyramide is an antiarrhythmic of Class 1a. Prescribing and monitoring should be guided by ECG and clinical context. Always check the BNF here or equivalent references for the latest recommendations.

About

• Disopyramide is a Class Ia antiarrhythmic agent.
• Has moderate sodium channel blockade and can prolong the QT interval.
• Used as an alternative or adjunct in specific arrhythmias, but it is not first-line post-MI.

Mode of Action

• Fast sodium channel inhibition: Decreases the rate of phase 0 depolarization in cardiac myocytes.
• Prolongs QT interval (and can prolong action potential duration), which may increase the risk of torsades de pointes.
• Has high protein binding.

Indications

• Ventricular tachycardia (VT) post–myocardial infarction, though not first-line.
• Hypertrophic cardiomyopathy (HCM) — can be used to reduce outflow tract obstruction.
• Main action is on the ventricles.

Contraindications

• Hypokalaemia (risk of arrhythmias, QT prolongation).
• Glaucoma (due to anticholinergic effects).
• Urinary retention.
• Pregnancy (seek specialist advice).
• Caution in:
  • Renal failure.
  • 2nd/3rd-degree AV block (unless pacemaker in place).
  • Sinus node disease.

Dose

• IV Administration (with continuous ECG monitoring):
  • Post-MI VT: 2 mg/kg slow IV over 5–10 minutes (max 150 mg).
• Oral Dosing:
  • Loading: up to 800 mg in the first 24 hours (in divided doses).
  • Maintenance: 300–800 mg/day in divided doses.
• Always monitor ECG and blood pressure; adjust dose based on clinical response and side effects.

Side Effects

• Negative inotropy: can precipitate or worsen heart failure; avoid in severe LV dysfunction.
• Anticholinergic effects: constipation, urinary retention, blurred vision, dry mouth.
• Can exacerbate glaucoma due to anticholinergic action.
• Bradycardia, conduction disturbances (e.g., AV block).

Interactions

• QT-prolonging drugs: Risk of additive QT prolongation (e.g., certain antiarrhythmics, macrolides, antipsychotics).
• Other negative inotropes (β-blockers, non-dihydropyridine calcium channel blockers): Increased risk of bradycardia and hypotension.
• Avoid concurrent anticholinergics if possible, to limit anticholinergic side effects.

References

• Summary of Product Characteristics