Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
NORPACE CR vs DISOPYRAMIDE PHOSPHATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Class Ia antiarrhythmic agent; decreases myocardial excitability and conduction velocity, and prolongs refractory period by blocking sodium channels.
Class Ia antiarrhythmic agent; inhibits cardiac sodium channels, prolongs action potential duration, increases effective refractory period, and reduces myocardial excitability and conduction velocity.
Treatment of documented life-threatening ventricular arrhythmias (e.g., sustained ventricular tachycardia),Off-label: prevention of atrial fibrillation recurrence, maintenance of sinus rhythm in atrial flutter
Treatment of life-threatening ventricular arrhythmias (e.g., sustained ventricular tachycardia),Suppression of symptomatic atrial fibrillation/flutter
Disopyramide controlled-release: 200 mg orally every 12 hours; maximum 400 mg/day.
100-200 mg orally every 6 hours; immediate-release: 100-200 mg every 6 hours; extended-release: 200-300 mg every 12 hours.
Terminal elimination half-life: 6-12 hours (normal renal function); prolonged to 12-20 hours in renal impairment. In coronary artery disease, half-life may be extended due to reduced clearance.
Terminal elimination half-life: 6-8 hours (normal renal function); prolonged to 15-25 hours in renal impairment (creatinine clearance <40 m L/min), requiring dose adjustment.
Primarily hepatic via CYP3A4; also excreted renally.
Primarily hepatic metabolism via CYP3A4; approximately 40-60% excreted unchanged in urine.
Renal (50-57% unchanged), hepatic metabolism (30-40%), fecal (<10%). Dose adjustment required for Cr Cl <40 m L/min.
Renal excretion of unchanged drug accounts for 40-60% of elimination; hepatic metabolism (N-dealkylation) accounts for 20-30%; approximately 10-15% excreted in feces via biliary elimination.
30-50% bound to albumin, alpha-1-acid glycoprotein, and lipoproteins.
50-65% bound to plasma proteins (primarily to alpha-1-acid glycoprotein, with lower affinity to albumin).
0.6-1.2 L/kg; larger Vd in heart failure (up to 2.0 L/kg) due to reduced tissue binding.
0.8-1.4 L/kg (extensive tissue distribution; higher in myocardial tissue than plasma).
Oral immediate-release: 70-80%; extended-release: 60-70% (first-pass metabolism). IV: 100%.
Oral: 80-90% (immediate-release); 60-80% (sustained-release due to incomplete absorption).
GFR 30-50 m L/min: 200 mg loading dose, then 100 mg every 12 hours. GFR 15-30 m L/min: 200 mg loading dose, then 100 mg every 24 hours. GFR <15 m L/min: 200 mg loading dose, then 100 mg every 48-72 hours.
GFR 30-50 m L/min: 100 mg every 8-12 hours; GFR 15-29 m L/min: 100 mg every 12-24 hours; GFR <15 m L/min or dialysis: 100 mg every 24 hours or 50 mg every 12 hours.
Child-Pugh Class B or C: Reduce dose by 50% and titrate carefully; monitor ECGs.
Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: avoid use or reduce by 75%.
Not recommended for pediatric use; safety and efficacy not established.
Children <1 year: 10-30 mg/kg/day divided every 6 hours; 1-4 years: 10-30 mg/kg/day divided every 6 hours; 4-12 years: 10-30 mg/kg/day divided every 6 hours; adolescents: same as adult dosing up to 400 mg/day.
Initiate at lower dose (e.g., 100 mg every 12 hours of controlled-release) due to increased risk of anticholinergic effects and renal impairment; monitor renal function and QT interval.
Start at low end of dosing range (100 mg every 6 hours) due to decreased renal function and increased sensitivity; monitor QTc interval and anticholinergic effects.
May cause widening of QRS complex and prolongation of QT interval, increasing risk of torsade de pointes and sudden death. Avoid use with other drugs that prolong QT interval. Use only for life-threatening arrhythmias.
Disopyramide has negative inotropic effects and may precipitate or exacerbate heart failure. Use with caution in patients with pre-existing heart failure or significant left ventricular dysfunction.
Can worsen arrhythmias (proarrhythmic); monitor ECG, electrolytes; adjust dose in renal/hepatic impairment; avoid in patients with pre-existing QT prolongation, hypokalemia, or bradycardia.
May worsen or precipitate heart failure due to negative inotropy,Risk of proarrhythmia (e.g., torsades de pointes) especially with hypokalemia or bradycardia,Anticholinergic effects: urinary retention, dry mouth, blurred vision, constipation,May cause hypoglycemia in rare cases,Dose adjustment required in renal or hepatic impairment
Pre-existing second- or third-degree AV block (unless pacemaker), cardiogenic shock, congenital QT prolongation, concurrent use of other QT-prolonging drugs, hypersensitivity to disopyramide.
Cardiogenic shock,Pre-existing second- or third-degree AV block (without pacemaker),Known hypersensitivity to disopyramide,Severe heart failure or left ventricular dysfunction
Avoid grapefruit juice as it may increase disopyramide levels. High-fat meals may delay absorption but do not significantly affect overall bioavailability; take consistently with or without food.
Avoid grapefruit juice as it may increase disopyramide concentrations. Limit caffeine intake as it may worsen arrhythmias. Avoid high-fat meals as they may reduce absorption.
FDA Pregnancy Category C. First trimester: Evidence of teratogenicity in animal studies (increased fetal resorption and skeletal abnormalities) but no adequate human studies. Second and third trimesters: May cause fetal bradycardia, hypoglycemia, and preterm labor due to beta-blockade effects; avoid use unless benefit outweighs risk.
Disopyramide crosses the placenta. First trimester: No well-controlled studies; potential for adverse effects based on animal data. Second and third trimesters: May stimulate uterine contractions, potentially causing preterm labor; reports of neonatal hypoglycemia and respiratory depression. Not recommended during pregnancy unless benefit outweighs risk.
Disopyramide is excreted in human breast milk; M/P ratio approximately 0.5-1.0. Limited data suggests low infant exposure but potential for hypoglycemia and bradycardia; caution advised. American Academy of Pediatrics considers disopyramide compatible with breastfeeding with monitoring.
Disopyramide is excreted into breast milk with milk-to-plasma ratio of approximately 0.9. Infant exposure estimated at 2–6% of maternal weight-adjusted dose. Monitor infant for bradycardia, hypoglycemia, and apnea. Weigh benefits against potential risks.
No formal dosing guidelines established. Pregnancy may alter pharmacokinetics (increased volume of distribution and clearance), potentially requiring dose adjustments. Therapeutic drug monitoring is recommended to maintain trough disopyramide levels between 2-5 mcg/m L. Due to proarrhythmic risks, use lowest effective dose and monitor closely.
Dose may require adjustment due to pregnancy-induced pharmacokinetic changes (increased volume of distribution, enhanced renal clearance, altered protein binding). Monitor serum disopyramide levels and therapeutic response; consider lower starting doses and titrate to effect.
NORPACE CR (disopyramide phosphate) is a Class Ia antiarrhythmic with strong anticholinergic effects; monitor for urinary retention, constipation, and dry mouth. It has negative inotropic effects and should be avoided in patients with compensated heart failure or cardiomyopathy. Dosage adjustment required in renal impairment (Cr Cl <40 m L/min). Therapeutic drug monitoring recommended (target 2-5 mcg/m L).
Disopyramide is a class IA antiarrhythmic with significant negative inotropic and anticholinergic effects. Avoid in patients with heart failure, cardiogenic shock, or glaucoma. Dose adjustment required in renal impairment. Monitor QRS and QT intervals; proarrhythmia risk. May cause hypoglycemia in elderly or diabetic patients. Therapeutic drug monitoring recommended (target 2-5 mcg/m L).
Do not crush or chew extended-release tablets; swallow whole.,Take at regular 12-hour intervals to maintain steady drug levels.,Avoid driving or operating machinery until you know how this medication affects you (may cause dizziness or blurred vision).,Report signs of hypoglycemia (sweating, shakiness) in diabetic patients, as disopyramide can lower blood sugar.,Maintain adequate fluid intake to prevent constipation.,Inform all healthcare providers you are taking this medication, especially before surgery or dental procedures.
Take exactly as prescribed; do not skip doses or double up.,Do not take with grapefruit juice.,Avoid alcohol and other CNS depressants.,Report symptoms of heart failure (shortness of breath, swelling) or arrhythmia (palpitations, syncope).,May cause dry mouth, blurred vision, urinary retention; use caution driving.,Monitor blood sugar if diabetic.,Do not stop abruptly without consulting your doctor.
No interactions on record
"Disopyramide, a class Ia antiarrhythmic agent, prolongs the QT interval by inhibiting cardiac potassium channels, thereby increasing the risk of torsades de pointes. Paroxetine, a selective serotonin reuptake inhibitor (SSRI), also has dose-dependent QT-prolonging effects, primarily through hERG channel blockade. Concomitant use synergistically lengthens the QT interval, predisposing patients to potentially fatal ventricular arrhythmias, especially in those with pre-existing risk factors such as hypokalemia, bradycardia, or genetic long QT syndrome."
"Disopyramide, a class Ia antiarrhythmic agent, prolongs ventricular repolarization by blocking cardiac sodium and potassium channels. Ezogabine, a potassium channel opener, also has dose-dependent effects on cardiac repolarization. Coadministration may result in additive QT interval prolongation, increasing the risk of torsade de pointes and other ventricular arrhythmias."
"Disopyramide, a class Ia antiarrhythmic agent, may potentiate the hypoglycemic effects of cinoxacin, a quinolone antibiotic, by enhancing insulin secretion and increasing peripheral glucose uptake. This interaction can lead to clinically significant hypoglycemia, particularly in patients with diabetes mellitus or those concurrently using other hypoglycemic agents. Patients may experience symptoms such as diaphoresis, palpitations, confusion, or loss of consciousness if blood glucose levels drop precipitously."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about NORPACE CR vs DISOPYRAMIDE PHOSPHATE, answered by our medical review team.
NORPACE CR is a Antiarrhythmic (Class Ia) that works by Class Ia antiarrhythmic agent; decreases myocardial excitability and conduction velocity, and prolongs refractory period by blocking sodium channels.. DISOPYRAMIDE PHOSPHATE is a Antiarrhythmic (Class Ia) that works by Class Ia antiarrhythmic agent; inhibits cardiac sodium channels, prolongs action potential duration, increases effective refractory period, and reduces myocardial excitability and conduction velocity.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between NORPACE CR and DISOPYRAMIDE PHOSPHATE depend on the specific clinical indication. These are both Antiarrhythmic (Class Ia) agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of NORPACE CR is: Disopyramide controlled-release: 200 mg orally every 12 hours; maximum 400 mg/day.. The standard adult dose of DISOPYRAMIDE PHOSPHATE is: 100-200 mg orally every 6 hours; immediate-release: 100-200 mg every 6 hours; extended-release: 200-300 mg every 12 hours.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between NORPACE CR and DISOPYRAMIDE PHOSPHATE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. NORPACE CR is classified as Category C. FDA Pregnancy Category C. First trimester: Evidence of teratogenicity in animal studies (increased fetal resorption and skeletal abnormalities) but no adequate human studies. Secon. DISOPYRAMIDE PHOSPHATE is classified as Category D/X. Disopyramide crosses the placenta. First trimester: No well-controlled studies; potential for adverse effects based on animal data. Second and third trimesters: May stimulate uteri. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.