Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
NORPACE CR vs NORPACE
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 Ic antiarrhythmic agent; blocks voltage-gated sodium channels, slowing conduction velocity and prolonging refractory periods in cardiac tissue.
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 documented life-threatening ventricular arrhythmias, such as sustained ventricular tachycardia,Off-label: Atrial fibrillation, atrial flutter, supraventricular tachycardia
Disopyramide controlled-release: 200 mg orally every 12 hours; maximum 400 mg/day.
150 mg orally every 6 hours (maximum 300 mg per dose), extended-release formulation 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 in renal impairment (up to 24 hours).
Primarily hepatic via CYP3A4; also excreted renally.
Extensively metabolized in the liver primarily by CYP2D6; also involves CYP1A2 and CYP3A4 to a minor extent. Active metabolite: desethylnorpace.
Renal (50-57% unchanged), hepatic metabolism (30-40%), fecal (<10%). Dose adjustment required for Cr Cl <40 m L/min.
Renal: 40-60% unchanged; biliary/fecal: minor (10-20%).
30-50% bound to albumin, alpha-1-acid glycoprotein, and lipoproteins.
80-90%, primarily to alpha-1-acid glycoprotein and albumin.
0.6-1.2 L/kg; larger Vd in heart failure (up to 2.0 L/kg) due to reduced tissue binding.
1.8-3.6 L/kg; large, indicating extensive tissue distribution.
Oral immediate-release: 70-80%; extended-release: 60-70% (first-pass metabolism). IV: 100%.
Oral: 80-90%.
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: 150 mg every 12-24 hours; GFR 15-29 m L/min: 150 mg every 24-48 hours; GFR <15 m L/min (not on dialysis): 150 mg every 48 hours or 100 mg every 24 hours.
Child-Pugh Class B or C: Reduce dose by 50% and titrate carefully; monitor ECGs.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 25-50% with monitoring; Child-Pugh Class C: contraindicated or use with extreme caution.
Not recommended for pediatric use; safety and efficacy not established.
<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; 12-18 years: 150-300 mg every 6 hours. Maximum 800 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.
Initiate at 100 mg every 6 hours; consider lower doses due to age-related renal decline; monitor for anticholinergic effects and QT prolongation.
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.
None
Can worsen arrhythmias (proarrhythmic); monitor ECG, electrolytes; adjust dose in renal/hepatic impairment; avoid in patients with pre-existing QT prolongation, hypokalemia, or bradycardia.
Proarrhythmic effects (e.g., new or worsened arrhythmias, torsades de pointes),Heart failure exacerbation,Hepatic impairment,Renal impairment,Electrolyte disturbances (hypokalemia, hypomagnesemia),Conduction disturbances (e.g., QT prolongation, heart block)
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.
Pre-existing second- or third-degree AV block unless pacemaker is present,Cardiogenic shock,Severe heart failure,QTc interval > 450 ms,Concomitant use of other QT-prolonging drugs,Hypersensitivity to disopyramide or any component
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.
Grapefruit juice may increase disopyramide levels; avoid concurrent intake. High-fat meals may delay absorption; take consistently with or without food. Avoid excessive alcohol, which can exacerbate hypotension and arrhythmias.
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.
First trimester: No evidence of increased risk of congenital malformations in human studies, but animal studies are insufficient. Second and third trimesters: Risk of fetal bradycardia, QT prolongation, and neonatal depression at delivery. Disopyramide may stimulate uterine contractions, increasing risk of preterm labor.
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 in breast milk with an M/P ratio of approximately 1:1.1. The relative infant dose is about 2–10% of the maternal weight-adjusted dose. Monitor infant for bradycardia, QT changes, and hypoglycemia. Alternative agents preferred unless benefit outweighs risk.
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.
Increased renal clearance and volume of distribution in pregnancy may reduce disopyramide serum concentrations. Therapeutic drug monitoring recommended; dose adjustments may be required to maintain efficacy, but empirical increases are not routinely recommended due to risk of uterine contractions and fetal effects. Plasma protein binding is unchanged.
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).
NORPACE (disopyramide) is a Vaughan Williams Class Ia antiarrhythmic with negative inotropic effects; avoid in patients with heart failure or reduced LVEF. Monitor QRS and QT intervals; torsades de pointes risk. Adjust dose in renal impairment. Anticholinergic side effects (dry mouth, urinary retention, blurred vision) are common.
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 miss doses or double up.,Avoid driving if you experience blurred vision or dizziness.,Report chest pain, shortness of breath, fainting, or rapid heartbeat immediately.,May cause dry mouth; sugarless gum or candy can help.,Avoid alcohol and grapefruit juice without consulting your doctor.,Do not stop abruptly; gradual tapering may be needed.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about NORPACE CR vs NORPACE, 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.. NORPACE is a Antiarrhythmic (Class Ia) that works by Class Ic antiarrhythmic agent; blocks voltage-gated sodium channels, slowing conduction velocity and prolonging refractory periods in cardiac tissue.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between NORPACE CR and NORPACE 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 NORPACE is: 150 mg orally every 6 hours (maximum 300 mg per dose), extended-release formulation 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 NORPACE 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. NORPACE is classified as Category C. First trimester: No evidence of increased risk of congenital malformations in human studies, but animal studies are insufficient. Second and third trimesters: Risk of fetal bradyca. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.