Disopyramide Phosphate
Disopyramide phosphate
Also known as: Norpace CR · Dicorantil · Dirythmin · Dirytmin · DisoDuriles · Disomet · Disonorm · Durbis · Isomide · Isorythm · Ritmodan · Ritmoforine · Rythmical · Rythmodan · Rythmodul · disopyramidi phosphas · SC-13957
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Antiarrhythmic (almost never used) | 7-30 mg/kg PO q4h | PO | q4h | — | 🌎 NA |
- Antiarrhythmic (almost never used): Considered a 2nd or 3rd line agent.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Disopyramide phosphate is a Class Ia (membrane-stabilizing) antiarrhythmic agent, structurally distinct but pharmacologically similar to quinidine and procainamide.
- Clinical Utility: It is rarely used in veterinary medicine (primarily considered a 2nd or 3rd line agent for dogs) due to its short half-life and potent negative inotropic effects.
- Key Characteristics: It reduces myocardial excitability and conduction velocity. Notably, it possesses significant anticholinergic (vagolytic) activity (150 mg of disopyramide is approximately equivalent to 0.09 mg of atropine), which heavily influences its side effect profile and contraindications.
- Cardiovascular Impact: While it generally has minimal effects on resting heart rates or blood pressure, it can increase systemic peripheral resistance by up to 20% and significantly depress myocardial contractility.
Mechanism of action
- Blocks fast inward sodium (Na⁺) channels → decreases the rate of phase 0 depolarization → slows conduction velocity through the atria and ventricles.
- Inhibits potassium (K⁺) channels → prolongs the action potential duration and increases atrial and ventricular refractory times.
- Decreases automaticity of ectopic atrial or ventricular pacemakers and shortens sinus node recovery time.
- Exerts a direct negative inotropic effect on the myocardium, reducing cardiac contractility.
- Possesses significant anticholinergic (vagolytic) activity, which can alter autonomic tone to the heart.
Safety & warnings
Contraindications
- Hypersensitivity to the drug
- 2nd or 3rd degree AV block (unless a pacemaker is inserted)
- Cardiogenic shock
- Severe uncompensated or poorly compensated cardiac failure
- Hypotension
- Glaucoma (closed-angle)
- Urinary retention
- Myasthenia gravis
Adverse effects
- Dry mouth, eyes, or nose
- Constipation
- Urinary hesitancy or retention
- Urinary frequency and urgency
- Edema
- Hypotension
- Dyspnea
- Syncope
- Conduction disturbances (e.g., AV block)
- Vomiting and diarrhea
- Intrahepatic cholestasis
- Hypoglycemia
- Fatigue and headache
- Muscle weakness and pain
- Prolonged QT interval (at 15 mg/kg q8h in dogs)
- Widened QRS complex (at doses >30 mg/kg in dogs)
Precautions
Use with extreme caution in patients with sick sinus syndrome, bundle branch block, or Wolff-Parkinson-White (WPW) syndrome. Patients with atrial fibrillation or flutter must be digitalized before disopyramide therapy to negate increased ventricular response. Use with caution (and possibly at a reduced dosage) in patients with hepatic or renal disease. Use with caution in nursing animals as the drug is excreted in milk.
Drug interactions
Additive anticholinergic effects may be encountered.
Additional prolongation of the QT interval.
Increased disopyramide levels; prolongation of QT interval may occur.
May increase disopyramide's metabolism and reduce serum levels.
May be used concurrently, but widening of QRS and prolongation of QT interval may occur.
May increase disopyramide levels; disopyramide may decrease quinidine levels.
May increase disopyramide's metabolism and reduce serum levels.
Because of additional negative inotropic effects, use of disopyramide within 48 hours of using verapamil is not recommended.
May cause additive negative inotropic effects.
Monitoring
- ECG (monitor for QT prolongation and QRS widening)
- Blood pressure
- Clinical signs of adverse effects (anticholinergic and cardiovascular)
- Liver function tests (if on chronic therapy)
- Serum drug levels (Therapeutic: 2-7 mcg/mL; Toxic: >9 mcg/mL)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed following oral administration. Oral bioavailability in dogs is about 70%.
Distribution
Distributed throughout the body in extracellular water and is not extensively bound to tissues. Plasma protein binding is variable and concentration-dependent (approximately 50-65% at therapeutic levels in humans). Crosses the placenta and enters milk.
Metabolism
Metabolized in the liver.
Elimination
40-65% is excreted unchanged in the urine. Dosage adjustments may be needed in renal disease to prevent accumulation.
Overdose
Clinical signs of toxicity: Anticholinergic effects, apnea, loss of consciousness, hypotension, cardiac conduction disturbances and arrhythmias, widening of the QRS complex and QT interval, bradycardia, congestive heart failure, seizures, asystole, and death.
Treatment:
- Initially consists of prompt gastric emptying, activated charcoal, and cathartics.
- Follow with vigorous symptomatic therapy using cardiac glycosides, vasopressors, sympathomimetics, diuretics, mechanically assisted respiration, and endocardial pacing if necessary.
- Disopyramide can be removed with hemodialysis.
Available products
Formulations
- Extended-release capsules
- Oral suspension (compounded)
Human-labeled
- Disopyramide Phosphate Capsules: 100 mg & 150 mg; Norpace® (Pharmacia); generic
- Disopyramide Phosphate Capsules Extended-Release: 100 mg & 150 mg; Norpace CR® (Pharmacia); generic
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules should be stored at room temperature (15-30°C) in well-closed containers. An extemporaneously prepared suspension of 1-10 mg/mL of disopyramide (from capsules) in cherry syrup has been shown to be stable for one month if stored in amber bottles and refrigerated (2-8°C).
Client information
Important: This medication must be given on a strict schedule due to how quickly it leaves your dog's body. Do not skip doses or double up on missed doses.
- Watch for side effects: Because of how this drug works, it can cause "drying" effects. Contact your veterinarian if your pet experiences dry mouth, dry eyes, constipation, or difficulty urinating.
- Monitor breathing and energy: If your pet becomes unusually lethargic, depressed, or has difficulty breathing, seek veterinary care immediately, as this could indicate an adverse effect on the heart's pumping ability or blood pressure.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.