disopyramide phosphate

disopyramide phosphate

[dī′sōpir′əmīd]

a cardiac antiarrhythmic.

indications It is prescribed in the treatment of atrial fibrillation, atrial flutter, ventricular premature complexes, and coupled ventricular tachycardias.

contraindications Cardiogenic shock, heart failure, preexisting second- or third-degree heart block in the absence of a pacemaker, sick sinus syndrome, or known hypersensitivity to this drug prohibits its use.

adverse effects Among the more serious adverse reactions are severe hypotension, precipitation of heart failure, and aggravation of heart block. Urinary retention, dry mouth, and constipation commonly occur.

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disopyramide phosphate

Norpace, Norpace CR

Pharmacologic class: Pyridine derivative

Therapeutic class: Ventricular and supraventricular antiarrhythmic (class IA), antitachyarrhythmic

Pregnancy risk category C

FDA Boxed Warning

• Drug has known proarrhythmic properties and doesn't improve survival in patients without life-threatening arrhythmias. Use only for patients with life-threatening ventricular arrhythmias.

Action

Slows diastolic depolarization rate, reduces upstroke velocity, and prolongs duration of action potential and refractory period. Also decreases disparity in refractoriness between infarcted and adjacent normally perfused myocardium.

Availability

Capsules: 100 mg, 150 mg

Capsules (extended-release): 100 mg, 150 mg

Tablets (extended-release): 150 mg

⊘Indications and dosages

➣ Ventricular tachycardia and other ventricular arrhythmias not severe enough to require cardioversion

Adults weighing more than 50 kg (110 lb): Initially, 200 to 300 mg P.O. as a loading dose, then 150 mg P.O. q 6 hours (conventional capsules) or 300 mg P.O. q 12 hours (extended-release forms)

Adults weighing 50 kg (110 lb) or less: 100 mg P.O. q 6 hours (conventional capsules) or 200 mg P.O. q 12 hours (extended-release capsules)

Children ages 12 to 18: 6 to 15 mg/kg P.O. daily in four divided doses given q 6 hours

Children ages 4 to 11: 10 to 15 mg/kg P.O. daily in four divided doses given q 6 hours

Children ages 1 to 3: 10 to 20 mg/kg P.O. daily in four divided doses given q 6 hours

Children younger than age 1: 10 to 30 mg/kg P.O. daily in four divided doses given q 6 hours

Dosage adjustment

• Renal or hepatic insufficiency
• Acute myocardial infarction

Off-label uses

• Paroxysmal supraventricular tachycardia

Contraindications

• Hypersensitivity to drug
• Cardiogenic shock
• Second- or third-degree heart block
• Sick sinus syndrome
• Congenital QT prolongation

Precautions

Use cautiously in:
• heart failure, left ventricular dysfunction, conduction abnormalities, hepatic or renal insufficiency, prostate enlargement, myasthenia gravis, glaucoma, diabetes mellitus
• pregnant or breastfeeding patients
• children.

Administration

• Start therapy 6 to 12 hours after last quinidine dose or 3 to 6 hours after last procainamide dose.
☞ Know that patient with atrial flutter or fibrillation should receive digitalis before starting disopyramide therapy to ensure that drug doesn't increase ventricular rate.

Route	Onset	Peak	Duration
P.O.	Rapid	2 hr	Unknown
P.O. (extended)	Unknown	4.9 ± 1.4 hr	Unknown
I.V.	Unknown	Unknown	Unknown

Adverse reactions

CNS: dizziness, agitation, depression, fatigue, headache, nervousness, acute psychosis, syncope

CV: chest pain, orthostatic hypotension, heart failure, heart block, arrhythmias

EENT: blurred vision, angle-closure glaucoma, dry eyes, dry nose

GI: nausea, vomiting, diarrhea, constipation, abdominal pain, bloating, flatulence, dry mouth

GU: urinary hesitancy or retention, erectile dysfunction

Hematologic: anemia, thrombocytopenia, agranulocytosis

Hepatic: jaundice

Metabolic: hypokalemia, hypoglycemia

Musculoskeletal: muscle weakness, myalgia

Respiratory: dyspnea

Skin: rash, pruritus, dermatoses

Other: edema, decreased appetite, weight gain

Interactions

Drug-drug. Antiarrhythmics, fluoroquinolones: widened QRS complex or QT interval

Anticholinergics: increased risk of adverse effects

Clarithromycin, erythromycin: increased disopyramide blood level

Phenytoin: increased disopyramide metabolism and decreased disopyramide blood level

Rifampin: decreased disopyramide blood level

Drug-diagnostic tests. Blood urea nitrogen, creatinine, hepatic enzymes, lipids: increased levels

Glucose, hematocrit, hemoglobin: decreased levels

Drug-herbs. Aloe, buckthorn bark or berry, cascara sagrada bark, senna pod or leaf: increased drug action

Jimsonweed: increased risk of adverse cardiovascular effects

Patient monitoring

• Check apical pulse before administering. Withhold dose if rate is below 60 or above 120 beats/minute.
• Monitor ECG for complete heart block.
☞ Assess closely for signs and symptoms of heart failure.
• Evaluate for signs and symptoms of fluid retention, such as rapid weight gain.
• Monitor electrolyte levels regularly, checking especially for hypokalemia.

Patient teaching

• Tell patient to weigh himself daily and report weekly gain of more than 2 lb (1 kg).
☞ Instruct patient to watch for and promptly report ankle swelling.
• Advise patient to move slowly when sitting up or standing, to avoid dizziness or light-headedness from sudden blood pressure decrease.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and herbs mentioned above.