DIGOXIN

DIGOXIN
(di-jox'in)
Lanoxicaps, Lanoxin
Classifications: cardiac glycoside; antiarrhythmic;
Therapeutic: cardiac glycoside
; antiarrhythmic
Pregnancy Category: C

Availability

0.05 mg, 0.1 mg, 0.2 mg capsules; 0.125 mg, 0.25 mg, 0.5 mg tablets; 0.05 mg/mL elixir; 0.25 mg/mL, 0.1 mg/mL injection

Action

Widely used cardiac glycoside of Digitalis lanata. Acts by increasing the force and velocity of myocardial systolic contraction (positive inotropic effect). It also decreases conduction velocity through the atrioventricular node. Action is more prompt and less prolonged than that of digitalis and digitoxin.

Therapeutic Effect

Increases the contractility of the heart muscle (positive inotropic effect). Has antiarrhythmic properties that result from its effects on the AV node.

Uses

Rapid digitalization and for maintenance therapy in CHF, atrial fibrillation, atrial flutter, paroxysmal atrial tachycardia.

Contraindications

Digitalis hypersensitivity, sick sinus syndrome, Wolff-Parkinson-White syndrome; ventricular fibrillation, ventricular tachycardia unless due to CHF. Full digitalizing dose not given if patient has received digoxin during previous week or if slowly excreted cardiotonic glycoside has been given during previous 2 wk.

Cautious Use

Renal insufficiency, hypokalemia, advanced heart disease, cardiomyopathy, acute MI, incomplete AV block, cor pulmonale; hypothyroidism; lung disease; premature and immature infants, children, older adults, or debilitated patients; pregnancy (category C).

Route & Dosage

Digitalizing Dose (Give ? dose initially followed by 1/4 at 8–12 h intervals)
Adult: PO 0.75–1.5 mg IV 0.5–1 mg
Child: IV 2–10 y, 20–35 mcg/kg; >10 y, 8–12 mcg/kg PO 2–10 y, 30–40 mcg/kg; >10y, 10–15 mcg/kg
Infant: IV 30–50 mcg/kg PO 35–60 mcg/kg
Neonate: IV Preterm, 15–25 mcg/kg; Full-term, 20–30 mcg/kg

Maintenance Dose
Adult: PO/IV 0.1–0.375 mg/d
Child: PO/IV <2 y, 7.5–9 mcg/kg/d; 2–10 y, 6–7.5 mcg/kg/d; >10 y, 0.125–0.25 mg/d
Neonate: IV 4–8 mcg/kg/d

Administration

Oral
  • Give without regard to food. Administration after food may slightly delay rate of absorption, but total amount absorbed is not affected.
  • Crush and mix with fluid or food if patient cannot swallow it whole.
Intravenous

PREPARE: Direct: Give undiluted or diluted in 4 mL of sterile water, D5W, or NS (less diluent may cause precipitation).  

ADMINISTER: Direct: Give each dose over at least 5 min.  

INCOMPATIBILITIES Solution/additive: Dobutamine. Y-site: Amiodarone, amphotericin B cholesteryl complex, fluconazole, foscarnet, propofol.

  • Store tablets, elixir, and injection solution at 25° C (77° F) or at 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CNS: Fatigue, muscle weakness, headache, facial neuralgia, mental depression, paresthesias, hallucinations, confusion, drowsiness, agitation, dizziness. CV: Arrhythmias, hypotension, AV block. Special Senses: Visual disturbances. GI: Anorexia, nausea, vomiting, diarrhea. Other: Diaphoresis, recurrent malaise, dysphagia.

Interactions

Drug: antacids, cholestyramine, colestipol decrease digoxin absorption; diuretics, corticosteroids, amphotericin B, laxatives, sodium polystyrene sulfonate may cause hypokalemia, increasing the risk of digoxin toxicity; calcium IV may increase risk of arrhythmias if administered together with digoxin; quinidine, verapamil, amiodarone, flecainide significantly increase digoxin levels, and digoxin dose should be decreased by 50%; erythromycin may increase digoxin levels; succinylcholine may potentiate arrhythmogenic effects; nefazodone may increase digoxin levels. Food: High fiber intake may decrease absorption. Herbal: Ginseng increase digoxin toxicity; ma huang, ephedra may induce arrhythmias; St. John's wort decreases plasma concentration.

Pharmacokinetics

Absorption: 70% PO tablets; 90% PO liquid and capsules. Onset: 1–2 h PO; 5–30 min IV. Peak: 6–8 h PO; 1–5 h IV. Duration: 3–4 d in fully digitalized patient. Distribution: Widely distributed; tissue levels significantly higher than plasma levels; crosses placenta. Metabolism: 14% in liver. Elimination: 80–90% by kidneys; may appear in breast milk. Half-Life: 34–44 h.

Nursing Implications

Assessment & Drug Effects

  • Take apical pulse for 1 full min, noting rate, rhythm, and quality before administering drug.
  • Withold medication and notify physician if apical pulse falls below ordered parameters (e.g., <50 or 60/min in adults and <60 or 70/min in children).
  • Be familiar with patient's baseline data (e.g., quality of peripheral pulses, blood pressure, clinical symptoms, serum electrolytes, creatinine clearance) as a foundation for making assessments.
  • Lab tests: Baseline and periodic serum digoxin, potassium, magnesium, and calcium. Draw blood samples for determining plasma digoxin levels at least 6 h after daily dose and preferably just before next scheduled daily dose.
  • Monitor for S&S of drug toxicity: In children, cardiac arrhythmias are usually reliable signs of early toxicity. Early indicators in adults (anorexia, nausea, vomiting, diarrhea, visual disturbances) are rarely initial signs in children.
  • Monitor I&O ratio during digitalization, particularly in patients with impaired renal function. Also monitor for edema daily and auscultate chest for rales.
  • Monitor serum digoxin levels closely during concurrent antibiotic–digoxin therapy, which can precipitate toxicity because of altered intestinal flora.
  • Observe patients closely when being transferred from one preparation (tablet, elixir, or parenteral) to another; when tablet is replaced by elixir potential for toxicity increases since ≥30% of drug is absorbed.

Patient & Family Education

  • Report to physician if pulse falls below 60 or rises above 110 or if you detect skipped beats or other changes in rhythm, when digoxin is prescribed for atrial fibrillation.
  • Suspect toxicity and report to physician if any of the following occur: Anorexia, nausea, vomiting, diarrhea, or visual disturbances.
  • Weigh each day under standard conditions. Report weight gain >1 kg (2 lb)/d.
  • Take digoxin PRECISELY as prescribed. Do not skip or double a dose or change dose intervals, and take it at same time each day.
  • Do not to take OTC medications, especially those for coughs, colds, allergy, GI upset, or obesity, without prior approval of physician.
  • Continue with brand originally prescribed unless otherwise directed by physician.

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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