Digoxin

 Action Increases force and velocity of myocardial systolic contraction (positive inotropic action), slows heart rate, and decreases conduction through atrioventricular node.

 Indications Treatment of CHF, atrial fibrillation, atrial flutter, paroxysmal atrial tachycardia, cardiogenic shock.

 Contraindications Ventricular fibrillation; ventricular tachycardia except in certain cases; digitalis toxicity; beriberi heart disease; hypersensitivity to digoxin; some cases of hypersensitive carotid sinus syndrome.

 Route/Dosage

ADULTS: Rapid digitalization with loading dose: IV 0.4 to 0.6 mg or PO tablets 0.5 to 0.75 mg or capsules 0.4 to 0.6 mg in previously undigitalized patients; additional doses may be given cautiously at 6 to 8 hr intervals (IV 0.1 to 0.3 mg or PO tablets 0.125 to 0.375 mg or capsules 0.1 to 0.3 mg) until clinical response is achieved; thereafter adjust dosage based on levels (usual range 0.125 to 0.5 mg/day as single daily dose). In previously digitalized patients, adjust dosage in proportion to ratio of desired vs current serum levels. INFANTS & CHILDREN: Rapid digitalization with loading dose: Individualize dosage. Usual pediatric doses are listed at end of section.

 Interactions

Amiodarone, anticholinergics, bepridol, benzodiazepines, ACE inhibitors, clarithromycin, cyclosporine, diltiazem, erythromycin, indomethacin, itraconazole, propafenone, quinidine, quinine, tetracycline, verapamil: May increase digoxin serum levels. Antacids, antineoplastics, cholestyramine, colestipol, kaolin/pectin, metoclopramide: May decrease absorption and effect of digoxin. Penicillamine: May decrease effect of digoxin. Potassium-sparing diuretics: May alter effect of digoxin. Thiazide or loop diuretics: May increase effect of digoxin. St. John's wort, thyroid hormones, thioamines: May decrease effect of digoxin.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Arrhythmias (supraventricular arrhythmias are more common in infants and children), including ventricular tachycardia and premature ventricular contractions. CNS: Headache; weakness; apathy; drowsiness; mental depression; confusion; disorientation. EENT: Visual disturbances (blurred vision, halo effect). GI: Anorexia; nausea; vomiting; diarrhea.

 Precautions

Pregnancy: Category C. Lactation: Excreted in breast milk. Children: Newborns show varying tolerance. Premature and immature infants are particularly sensitive; reduce and individualize dose as needed. Elderly: Use with caution; renal clearance likely to be reduced. Cardiovascular disease: Electrical conversion of arrhythmias may require dose reduction. Digitalis toxicity: Anorexia, nausea, and vomiting may be associated with toxicity or CHF. Arrhythmias for which digoxin is indicated may also be a reflection of toxicity. Impaired renal function: Excretion may be decreased, leading to digoxin accumulation and toxicity; adjust dosage. Electrolyte imbalance: Maintain normal serum potassium, calcium, and magnesium levels. Lanoxicaps: Have greater bioavailability than standard tablets. The 0.2 mg capsule is equivalent to 0.25 mg tablet; the 0.1 mg capsule to 0.125 mg tablet; the 0.05 mg capsule to 0.0625 mg tablet.

 Administration/Storage

• Administer IM doses deep into gluteal muscles and massage well to reduce painful, local reactions. IM route should be avoided; use only when other routes not available.
• Do not use solutions that are discolored or contain precipitate if dilution for IV administration is desired.
• For IV administration, digoxin injection may be diluted (up to 4-fold) with normal saline, D5W, or Sterile Water for Injection. Infuse slowly, over 5 min or longer.
• Do not mix digoxin solution with other drugs.
• Before administering loading dose, determine if patient has taken digoxin or other digitalis preparation in past 2 wks.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Monitor apical pulse for 1 full min before administering. Withhold dose and notify physician if pulse rate is < 60 bpm in adult, < 70 bpm in child, or < 90 bpm in infant.
• Assess for peripheral edema and auscultate lungs for rales/crackles before and throughout therapy.
• Plan for dosage adjustments when changing from parenteral to oral (and vice versa) route of administration.
• Notify physician if signs of toxicity occur (eg, abdominal pain, anorexia, nausea, vomiting, visual disturbance, bradycardia, ECG changes, arrhythmias, headache, seizure). Be prepared to administer digoxin antibodies (digoxin-immune Fab) for severe overdose toxicity.
• Measure and record patient's daily weight and I&O.
• Monitor serum electrolyte levels, renal and hepatic function studies, and digoxin serum levels and report changes to physician.

 Patient/Family Education

• Instruct patient to take digoxin at same time each day to ensure steady-state dosing and to contact physician for instructions if dose is missed.
• Teach patient and family name, action, administration, side effects, and toxic effects of particular digoxin preparation.
• Emphasize importance of regular follow-up exams to determine effectiveness and to monitor for toxicity.
• Caution patient to avoid taking otc medications without consulting physician. Antacids and antidiarrheals, for example, slow absorption of digoxin.
• Teach patient and family to take pulse and to seek physician's advice for rates lower than 60 bpm or higher than 100 bpm (adults).
• If patient is directed by physician, help identify ways to supplement potassium intake.