Disopyramide phosphate
Disopyramide phosphate (Norpace)
Disopyramide phosphate
(dye-so- PEER-ah-myd)
Pregnancy Category: C Norpace Norpace CR Rythmodan-LA (Rx)

Classification: Antiarrhythmic, class IA

Action/Kinetics: Decreases the rate of diastolic depolarization (phase 4), decreases the upstroke velocity (phase 0), increases the action potential duration (of normal cardiac cells), and prolongs the refractory period (phases 2 and 3). Weak anticholinergic effects; fewer side effects than quinidine. Does not affect BP significantly; can be used in digitalized and nondigitalized clients. Onset: 30 min. Peak plasma levels: 2 hr. Duration: average of 6 hr (range 1.5-8 hr). t 1/2: 4-10 hr. Therapeutic serum levels: 2-4 mcg/mL. Do not use serum levels to adjust the dose because of variance in protein binding and potential toxicity of unbound drug. Protein binding: 40%-60%. Bioavailability of the controlled-release capsules appears to be similar to that of the immediate-release capsules. Both unchanged drug (50%) and metabolites (30%) are excreted through the urine. Approximately 15% is excreted through the bile.

Uses: Life-threatening ventricular arrhythmias (e.g., sustained ventricular tachycardia). Not been shown to improve survival in clients with ventricular arrhythmias. Investigational: Paroxysmal SVT.

Contraindications: Hypersensitivity to drug. Cardiogenic shock, heart failure, heart block (especially preexisting second- and third-degree AV block if no pacemaker is present), congenital QT prolongation, asymptomatic ventricular premature contractions, sick sinus syndrome, glaucoma, urinary retention, myasthenia gravis. Use of controlled-release capsules in clients with severe renal insufficiency. Lactation.

Special Concerns: Safe use during childhood, labor, and delivery has not been established. Use with caution in Wolff-Parkinson-White syndrome or bundle branch block. Decrease dosage in impaired hepatic function. Geriatric clients may be more sensitive to the anticholinergic effects of this drug. The drug may be ineffective in hypokalemia and toxic in hyperkalemia.

Side Effects: Increased risk of death when used in clients with non-life-threatening cardiac arrhythmias. CV: Hypotension, CHF, worsening of arrhythmias edema, weight gain, cardiac conduction disturbances, SOB, syncope, chest pain, AV block, severe myocardial depression (with hypotension and increased venous pressure). Anticholinergic: Dry mouth, urinary retention, constipation, blurred vision, dry nose, eyes, and throat. GU: Urinary frequency and urgency, urinary retention, impotence, dysuria. GI: Nausea, pain, flatulence, anorexia, diarrhea, vomiting, severe epigastric pain. CNS: Headache, nervousness, dizziness, fatigue, depression, insomnia, psychoses. Dermatologic: Rash, dermatoses, itching. Other: Fever, respiratory problems, gynecomastia, anaphylaxis malaise, muscle weakness, numbness, tingling, angle-closure glaucoma, hypoglycemia, reversible cholestatic jaundice, symptoms of lupus erythematosus (usually in clients switched to disopyramide from procainamide).

Laboratory Test Alterations: Creatinine, BUN, cholesterol, triglycerides, and liver enzymes.

Overdose Management: Symptoms: Apnea, loss of consciousness, cardiac arrhythmias (widening of QRS complex and QT interval, conduction disturbances), hypotension, bradycardia, anticholinergic symptoms, loss of spontaneous respiration, death. Treatment: Induction of vomiting, gastric lavage, or a cathartic followed by activated charcoal. Monitor ECG. IV isoproterenol, IV dopamine, cardiac glycosides, diuretics, intra-aortic balloon counterpulsation, artificial respiration, hemodialysis. Use endocardial pacing to treat AV block and neostigmine to treat anticholinergic symptoms.

Drug Interactions: Anticoagulants / PT after discontinuing disopyramide Beta-adrenergic blockers / Possible clearance of disopyramide; sinus bradycardia, hypotension Digoxin / Serum digoxin levels (may be beneficial) Erythromycin / Disopyramide levels arrhythmias and QTc intervals Phenytoin / Effect R/T liver breakdown; anticholinergic effects Quinidine / Disopyramide serum levels or quinidine levels Rifampin / effect R/T liver breakdown

How Supplied: Capsule: 100 mg, 150 mg; Capsule, Extended Release: 100 mg, 150 mg

Dosage
?Immediate-Release Capsules Antiarrhythmic.
Adults, initial loading dose: 300 mg of immediate-release capsule (200 mg if client weighs less than 50 kg); maintenance: 400-800 mg/day in four divided doses (usual: 150 mg q 6 hr). For clients less than 50 kg, maintenance: 100 mg q 6 hr. Children, less than 1 year: 10-30 mg/kg/day in divided doses q 6 hr; 1-4 years of age: 10-20 mg/kg/day in divided doses q 6 hr; 4-12 years of age: 10-15 mg/kg/day in divided doses q 6 hr; 12-18 years of age: 6-15 mg/kg/day in divided doses q 6 hr.
Severe refractory tachycardia.
Up to 400 mg q 6 hr may be required.
Cardiomyopathy.
Do not administer a loading dose; give 100 mg q 6 hr of immediate-release or 200 mg q 12 hr for controlled-release.
?Extended-Release Capsules Antiarrhythmic, maintenance only.
Adults: 300 mg q 12 hr (200 mg q 12 hr for body weight less than 50 kg).
NOTE: For all uses, decrease dosage in clients with renal or hepatic insufficiency.
Moderate renal failure or hepatic failure.
100 mg q 6 hr (or 200 mg/12 hr of sustained-release form).
Severe renal failure.
100 mg q 8-24 hr depending on severity (with or without an initial loading dose of 150 mg).