Disopyramide
NORPACE
What it isClass IA antiarrhythmic with marked antimuscarinic action; ventricular arrhythmia and hypertrophic obstructive cardiomyopathy.
Why this oneIts negative inotropy is exploited deliberately to reduce outflow obstruction in HOCM.
What limits itHeavy anticholinergic burden — retention, dry mouth, glaucoma. Proarrhythmia; avoid in heart failure.
FDA-approved for
- ventricular arrhythmias (1977)
Off-label
- hypertrophic obstructive cardiomyopathy
FDA label
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| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Life-threatening ventricular arrhythmia | Adult ≥50 kg | 150 mg q6h (600 mg/day); optional 300 mg load | 600 mg/day divided (400–800 mg/day range) | 1600 mg/day (400 mg q6h; hospitalized, refractory) |
| Life-threatening ventricular arrhythmia | Adult <50 kg (<110 lb) | 100 mg q6h (400 mg/day); optional 200 mg load | 400 mg/day divided | 1600 mg/day (hospitalized, refractory) |
| Ventricular arrhythmia, with cardiomyopathy or possible cardiac decompensation | Adult | 100 mg q6–8h, no loading dose | titrate gradually | |
| Ventricular arrhythmia | Pediatric (divided q6h) | <1 yr 10–30, 1–4 yr 10–20, 4–12 yr 10–15, 12–18 yr 6–15 mg/kg/day |
Renal Moderate (CrCl >40 mL/min): 100 mg q6h (400 mg/day). Severe (CrCl ≤40): 100 mg at extended intervals — q8h (30–40), q12h (15–30), q24h (<15), ± 150 mg load.
Hepatic Hepatic insufficiency: 100 mg q6h (400 mg/day).
Instructions
- Individualize to response and tolerance
- When transferring from quinidine or procainamide, start maintenance schedule without a loading dose 6–12 h after last quinidine or 3–6 h after last procainamide
Contraindications
- Cardiogenic shock
- Preexisting second- or third-degree AV block without a pacemaker
- Congenital QT prolongation
Cautions
- Proarrhythmia
- Hypotension and congestive heart failure (negative inotrope)
- Anticholinergic effects, including urinary retention
- Hypoglycemia
- QT prolongation / conduction disturbances
Adverse reactions
- Dry mouth, urinary hesitancy, constipation, blurred vision
- Urinary retention, urinary frequency/urgency
- Nausea, abdominal pain/bloating
- Dizziness, fatigue/muscle weakness, headache
- Hypotension with or without CHF
- Hypoglycemia
Pregnancy No adequate studies; use only if benefit justifies risk; animal effects on implantation and pup survival; stimulates uterine contractions.
Lactation Undefined
⚠ BOXED WARNING
- Increased mortality in asymptomatic PVCs
Cost, est. cash$10–$300/month
Generic entry1985
Classes and tags
Clinical profile
Legacy pregnancy categoryC
Defining liabilityAnticholinergic effects, negative inotropy and QT prolongation; overdose can cause shock and dysrhythmia.
Mechanism of action: Disopyramide ballicule
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