Home Drug Guide Disopyramide Phosphate

Drug Guide

Generic Name

Disopyramide Phosphate

Brand Names Norpace, Norpace CR

Classification

Therapeutic: Antiarrhythmic agent

Pharmacological: Class 1A Sodium channel blocker

FDA Approved Indications

Ventricular arrhythmias
Supraventricular arrhythmias

Mechanism of Action

Disopyramide inhibits sodium channels during phase 0 of the cardiac action potential, reducing excitability and conduction velocity, thereby suppressing abnormal electrical activity in the heart.

Dosage and Administration

Adult: Initial dose typically 300-600 mg per day in divided doses; dosage adjusted based on patient response and tolerability.

Pediatric: Limited data; use is generally not recommended due to safety concerns.

Geriatric: Start at lower doses; monitor closely due to increased risk of adverse effects.

Renal Impairment: Adjust dose in severe impairment; consult specific guidelines.

Hepatic Impairment: Use cautiously; no specific adjustments well established.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Widely distributed; crosses the placenta.

Metabolism: Minimally metabolized in the liver.

Excretion: Primarily excreted unchanged in urine.

Half Life: Approximately 4-7 hours in healthy individuals.

Contraindications

2nd or 3rd degree AV block
Sick sinus syndrome unless a pacemaker is in place
Severe CHF
Hypersensitivity to disopyramide

Precautions

Use cautiously in patients with glaucoma, urinary retention, myasthenia gravis, or electrolyte imbalances such as hypokalemia or hypomagnesemia.

Adverse Reactions - Common

Anticholinergic side effects (dry mouth, urinary retention, constipation, blurred vision) (Common)

Adverse Reactions - Serious

Arrhythmias, including QT prolongation and torsades de pointes (Serious and potentially life-threatening)
Heart failure (Serious)

Drug-Drug Interactions

Other antiarrhythmic agents (risk of additive effects)
CNS depressants (enhanced sedative effects)
Potassium-wasting diuretics (risk of electrolyte disturbances)

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor ECG for arrhythmias, blood pressure, HR, electrolyte levels, and signs of anticholinergic toxicity.

Diagnoses:

Risk for arrhythmias
Impaired cardiac output
Potential for drug toxicity

Implementation: Administer with food to decrease gastrointestinal upset, observe for adverse effects, especially during dose titration.

Evaluation: Assess for resolution or improvement of arrhythmias, monitor for adverse effects.

Patient/Family Teaching

Do not abruptly discontinue medication.
Report symptoms of arrhythmias, vision changes, or severe side effects.
Maintain hydration and electrolyte balance.
Use caution with activities that require alertness due to anticholinergic effects.

Special Considerations

Black Box Warnings:

Potential for proarrhythmia, including torsades de pointes

Genetic Factors: Genetic variation in drug metabolism may affect response.

Lab Test Interference: None noted.

Overdose Management

Signs/Symptoms: Severe anticholinergic effects, heart conduction disturbances, arrhythmias, hypotension.

Treatment: Supportive care, activated charcoal if ingested recently, correction of electrolyte imbalances, cardiac monitoring, and administration of adult-specific interventions such as atropine for bradycardia or pace-maker support if indicated.

Storage and Handling

Storage: Store at room temperature, away from moisture and light.

Stability: Stable under recommended storage conditions.