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Class Ia antiarrhythmic Pregnancy: Avoid unless essential — uterotonic effect (preterm labour); limited safety data.

Disopyramide

Brand names: Rythmodan, Norpace

Adult dose

Dose: Loading: 300 mg PO. Maintenance: 100–200 mg every 6 hours (immediate-release) or 250–375 mg BD (Rythmodan Retard CR). IV (specialist): 2 mg/kg over 5 min, max 150 mg, then 0.4 mg/kg/h.
Route: Oral / IV
Frequency: Every 6 hours (IR) or BD (CR)
Max: 800 mg/day
Rarely initiated outside specialist cardiology. Hospital initiation with telemetry recommended. Rebound after stopping — taper.

Dose adjustments

Renal

eGFR 30–59: max 100 mg every 8 hours. eGFR 15–29: 100 mg every 12 hours. eGFR <15: 100 mg every 24 hours.

Hepatic

Reduce dose 50%; monitor closely.

Clinical pearls

  • Niche specialist use: hypertrophic obstructive cardiomyopathy (HOCM) for relief of dynamic LVOT obstruction — disopyramide's negative inotropy reduces gradient (Maron studies; ESC HCM Guidelines 2014/2023).
  • Also occasional use for vagally-mediated paroxysmal AF (countering vagal dominance) and for paroxysmal SVT in select cases.
  • Largely superseded by safer Class Ic agents (flecainide) or Class III (amiodarone, sotalol) for general arrhythmia management.
  • Powerful anticholinergic activity — limits use in elderly, men with BPH, and patients with glaucoma. Cardiologists frequently combine with pyridostigmine to mitigate side effects in HOCM.
  • Hypoglycaemia is an unusual but described side effect — particularly in elderly with renal impairment.
  • Always check baseline ECG (QT), K+, Mg2+ before initiation; monitor QT during titration.

Contraindications

  • Cardiogenic shock
  • Sinoatrial node dysfunction or 2nd/3rd degree AV block (without pacemaker)
  • Pre-existing QT prolongation or congenital long QT
  • Severe heart failure (negative inotrope — especially without preserved EF)
  • Hypokalaemia, hypomagnesaemia (correct before use)
  • Narrow-angle glaucoma
  • Urinary retention, BPH (anticholinergic effect)
  • Myasthenia gravis

Side effects

  • Anticholinergic: dry mouth, blurred vision, urinary retention, constipation, BPH worsening
  • Negative inotropy — heart failure precipitation
  • QT prolongation, torsades de pointes
  • Bradycardia, AV block
  • Hypotension (especially IV)
  • Hypoglycaemia (uncommon — non-insulinoma hypoglycaemia)
  • Nausea, GI upset
  • Cholestatic jaundice (rare)

Interactions

  • Other QT-prolonging drugs (amiodarone, citalopram, sotalol, methadone, ondansetron): ↑ TdP risk
  • CYP3A4 inhibitors (clarithromycin, ketoconazole, ritonavir): ↑ disopyramide levels — caution
  • CYP3A4 inducers (rifampicin, phenytoin): ↓ levels
  • Beta-blockers, verapamil, diltiazem: additive negative inotropy and bradycardia
  • Other anticholinergics: additive antimuscarinic toxicity
  • Hypokalaemic agents (loop/thiazide diuretics, corticosteroids): correct K before use

Monitoring

  • ECG (QT, QRS) at baseline, after each dose change, then 6-monthly
  • U&Es, K+, Mg2+
  • FBC and LFTs annually
  • Glucose (especially elderly/renal impairment)

Reference: BNF 90; SmPC Rythmodan; ESC HCM Guidelines 2023; ESC AF Guidelines 2024. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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