Last reviewed 2026-04-20 · How we verify

Norpace Cr (Disopyramide Phosphate)

Norpace is a sodium channel blocker and a Class 1a anti-arrhythmic agent.

Disopyramide phosphate is indicated for treatment of documented life-threatening ventricular arrhythmias such as sustained ventricular tachycardia. The drug carries significant risks including hypotension, congestive heart failure, and anticholinergic effects, with urinary retention being the most serious anticholinergic adverse effect. Major drug interactions exist with CYP3A4 inhibitors (clarithromycin, erythromycin, ketoconazole) that can result in life-threatening complications, and verapamil must be avoided within specific timeframes. Hospital initiation is required due to proarrhythmic potential and serious adverse reaction profile.

At a glance

Mechanism of action

Norpace works by blocking sodium channels in the heart, which helps to regulate the heart's rhythm. This is achieved through its mechanism of action as a Class 1a anti-arrhythmic agent. By blocking sodium channels, Norpace decreases the rate of diastolic depolarization and upstroke velocity, and increases the action potential duration of normal cardiac cells.

Approved indications

• Documented ventricular arrhythmias
• Sustained ventricular tachycardia
• Life-threatening ventricular arrhythmias

Boxed warnings

• Mortality In the National Heart, Lung and Blood Institute's Cardiac Arrhythmia Suppression Trial (CAST), a long-term, multi-center, randomized, double-blind study in patients with asymptomatic non-life-threatening ventricular arrhythmias who had had a myocardial infarction more than 6 days but less than 2 years previously, an excessive mortality or non-fatal cardiac arrest rate (7.7%) was seen in patients treated with encainide or flecainide compared with that seen in patients assigned to carefu

Common side effects

• Headache
• Dizziness
• Bursitis
• Arthralgia
• Diarrhoea
• Bowel movement irregularity
• Nausea
• Anxiety
• Insomnia
• Atrial fibrillation
• Palpitations
• Pain in extremity

Serious adverse events

• Hypotension
• Stress cardiomyopathy
• Syncope
• Acute respiratory failure
• Pulmonary oedema
• Acute coronary syndrome
• Back pain
• Atrial fibrillation
• Cardiac arrest
• Myasthenia gravis

Drug interactions

• Phenytoin and other hepatic enzyme inducers
• Other antiarrhythmic drugs (quinidine, procainamide, lidocaine, propranolol)
• Verapamil
• Clarithromycin and erythromycin
• Ketoconazole and other potent CYP3A4 inhibitors

Primary sources

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