DISOPYRAMIDE PHOSPHATE

DISOPYRAMIDE PHOSPHATe
(dye-soe-peer'a-mide)
Napamide, Norpace, Norpace CR, Rythmodan

, Rythmodan-LA

Classifications: antiarrhythmic, class ia;
Therapeutic: antiarrhythmic, class ia
Prototype: Procainamide
Pregnancy Category: C

Availability

100 mg, 150 mg regular and sustained release capsules

Action

Class IA antiarrhythmic agent that decreases myocardial conduction velocity and excitability in the atria, ventricles, and accessory pathways. It prolongs the QRS and QT intervals in normal sinus rhythm and artial arrhythmias.

Therapeutic Effect

Acts as myocardial depressant by reducing rate of spontaneous diastolic depolarization in pacemaker cells, thereby suppressing ectopic focal activity.

Uses

To suppress and prevent recurrence of premature ventricular contractions (unifocal, multifocal, paired) and ventricular tachycardia not severe enough to require cardioversion.

Unlabeled Uses

In combination with other antiarrhythmic drugs to treat or prevent serious refractory arrhythmias. To convert atrial fibrillation, atrial flutter, and paroxysmal atrial tachycardia to normal sinus rhythm.

Contraindications

Cardiogenic shock, preexisting 2nd or 3rd degree AV block (if no pacemaker is present); sick sinus syndrome (bradycardia-tachycardia); Wolff-Parkinson-White (WPW) syndrome or bundle branch block, history of torsades de pointes; cardiogenic shock; QT prolongation; uncompensated or inadequately compensated CHF, hypotension (unless secondary to cardiac arrhythmia), hypokalemia; pregnancy (category C).

Cautious Use

Myocarditis or other cardiomyopathy, underlying cardiac conduction abnormalities; hepatic or renal impairment; urinary tract disease (especially prostatic hypertrophy); diabetes mellitus; myasthenia gravis; elderly; narrow-angle glaucoma; family history of glaucoma; lactation.

Route & Dosage

Arrhythmias
Adult: PO <50 kg, 100 mg q6h or 200 mg sustained release q12h; >50 kg, 100–200 mg q6h or 300 mg sustained release capsule q12h
Child: PO <1 y, 10–30 mg/kg/d in divided doses q6h; 1–4 y, 10–20 mg/kg/d in divided doses q6h; 4–12 y, 10–15 mg/kg/d in divided doses q6h; 12–18 y, 6–15 mg/kg/d in divided doses q6h

Administration

Oral

Start drug 6–12 h after last quinidine dose and 3–6 h after last procainamide dose for patients who have been receiving either quinidine or procainamide.
Give sustained release capsules whole.
Do not use sustained release capsules in loading doses when rapid control is required or in patients with creatinine clearance of ≤40 mL/min.
Start sustained release capsules 6 h after last dose of conventional capsule if change in drug form is made.
Store at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity (pruritus, urticaria, rash, photosensitivity, laryngospasm). CNS: Dizziness, headache, fatigue, muscle weakness, convulsions, paresthesias, nervousness, acute psychosis, peripheral neuropathy. CV: Hypotension, chest pain, edema, dyspnea, syncope, bradycardia, tachycardia; worsening of CHF or cardiac arrhythmia; cardiogenic shock, heart block; edema with weight gain. Special Senses: Blurred vision, dry eyes, increased IOP, precipitation of acute angle-closure glaucoma. GI: Dry mouth, constipation, epigastric or abdominal pain, cholestatic jaundice. Urogenital: Hesitancy and retention, urinary frequency, urgency, renal insufficiency. Other: Dry nose and throat, drying of bronchial secretions, initiation of uterine contractions (pregnant patient); muscle aches, precipitation of myasthenia gravis, agranulocytosis (rare), thrombocytopenia.

Interactions

Drug: anticholinergic drugs (e.g., tricyclic antidepressants, antihistamines) compound anticholinergic effects; other antiarrhythmics compound toxicities; phenytoin, rifampin may increase disopyramide metabolism and decrease levels; may increase warfarin-induced hypoprothrombinemia.

Pharmacokinetics

Absorption: Readily from GI tract; 60–83% reaches systemic circulation. Onset: 30 min–3.5 h. Peak: 1–2 h. Duration: 1.5–8.5 h. Distribution: Distributed in extracellular fluid; crosses placenta; distributed into breast milk. Metabolism: In liver. Elimination: 80% in urine, 10% in feces. Half-Life: 4–10 h.

Nursing Implications

Assessment & Drug Effects

Check apical pulse before administering drug. Withhold drug and notify physician if pulse rate is slower than 60 bpm, faster than 120 bpm, or if there is any unusual change in rate, rhythm, or quality.
Monitor ECG closely. The following signs are indications for drug withdrawal: Prolongation of QT interval and worsening of arrhythmia interval, QRS widening (>25%).
Monitor for rapid weight gain or other signs of fluid retention.
Lab tests: Baseline and periodic hepatic and renal function tests, blood glucose, and serum potassium. Correct hypokalemia or other imbalances before initiation of therapy.
Monitor BP closely in all patients during periods of dosage adjustment and in those receiving high dosages.
Monitor I&O, particularly in older adults and patients with impaired renal function or prostatic hypertrophy. Persistent urinary hesitancy or retention may necessitate lower dosage or discontinuation of drug.
Report S&S of hyperkalemia (see Appendix F); it enhances drug's toxic effects.
Measure IOP before treatment begins in patients with a family history of glaucoma.
Monitor for S&S of CHF.
Discontinue promptly if S&S of agranulocytosis, peripheral neuritis, or jaundice appear (see Appendix F).

Patient & Family Education

Take drug precisely as prescribed to maintain regularity of heartbeat. Do not skip or stop medication or change dose without consulting physician.
Weigh daily under standard conditions and check ankles for edema. Report to physician a weekly weight gain of ≥1–2 kg (2–4 lb).
Make position changes slowly, particularly when getting up from lying down because of the possibility of hypotension; dangle legs for a few minutes before walking, and do not stand still for prolonged periods. If you feel light-headed, lie down or sit down.
Do not take OTC medications unless approved by physician.
Avoid exposure to sunlight or ultraviolet light; drug may cause photosensitivity.
Do not drive or engage in other potentially hazardous activities until response to drug is known.
Do not drink alcoholic beverages while taking disopyramide.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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