Drug Guide
Digitoxin
Classification
Therapeutic: Cardiac glycoside used in heart failure and atrial fibrillation
Pharmacological: Inhibits Na+/K+-ATPase enzyme
FDA Approved Indications
- Heart failure associated with reduced ejection fraction
- Atrial fibrillation or flutter
Mechanism of Action
Digitoxin inhibits the sodium-potassium ATPase pump, leading to increased intracellular calcium in cardiac cells, which enhances cardiac contractility (positive inotropic effect). It also exerts effects on the parasympathetic nervous system, reducing conduction through the AV node.
Dosage and Administration
Adult: Typical starting dose: 0.075 mg per day, adjusted based on response and toxicity; dosage varies with patient condition.
Pediatric: Use is limited; consult specialist.
Geriatric: Start at lower doses due to increased sensitivity and decreased clearance.
Renal Impairment: Adjust dose downward; monitor serum levels.
Hepatic Impairment: Use with caution; no specific dose adjustment provided.
Pharmacokinetics
Absorption: Well absorbed from gastrointestinal tract.
Distribution: Widely distributed, crosses placenta; serum protein binding approx. 25%.
Metabolism: Primarily hepatic metabolism, some renal excretion.
Excretion: Excreted mainly via urine.
Half Life: 7-9 days, which allows for once-daily dosing.
Contraindications
- Ventricular fibrillation
- Uncontrolled AV block without pacemaker
Precautions
- Use with caution in renal impairment, hypokalemia, hypomagnesemia, or hypothyroidism. Monitor serum electrolyte levels and renal function regularly. Increased risk of toxicity in these conditions.
Adverse Reactions - Common
- Nausea and vomiting (Common)
- Dizziness or fatigue (Common)
- Visual disturbances (yellow or green halos) (Less common)
Adverse Reactions - Serious
- Digitalis toxicity leading to arrhythmias (Serious)
- AV block or other arrhythmias (Serious)
Drug-Drug Interactions
- Other arrhythmics, diuretics causing electrolyte imbalance, corticosteroids, certain antibiotics
Drug-Food Interactions
- Excessive alcohol, high-fat meals may alter absorption
Drug-Herb Interactions
- St. John's Wort may reduce effectiveness
Nursing Implications
Assessment: Monitor cardiac rhythm, serum electrolytes, renal and hepatic function, signs of toxicity.
Diagnoses:
- Risk for arrhythmias related to electrolyte imbalance or toxicity.
Implementation: Administer as prescribed; monitor serum digitoxin levels to stay within therapeutic range (10-30 ng/mL). Adjust dose based on response and toxicity risk.
Evaluation: Assess for improvement in heart failure symptoms, monitor for adverse effects.
Patient/Family Teaching
- Take medication exactly as prescribed.
- Do not discontinue abruptly.
- Be aware of signs of toxicity: nausea, vomiting, visual changes, arrhythmias.
- Report any irregular heartbeat or dizziness.
Special Considerations
Black Box Warnings:
- Toxicity can be life-threatening; narrow therapeutic index.
Genetic Factors: Genetic variations in metabolizing enzymes may impact drug levels.
Lab Test Interference: Serum digitoxin levels may be affected by other lab testing; interpret with caution.
Overdose Management
Signs/Symptoms: Nausea, vomiting, confusion, visual disturbances, arrhythmias, bradycardia.
Treatment: Discontinue digitoxin, treat symptoms supportively, administer activated charcoal if ingestion was recent, consider digoxin-specific antibody fragments if severe toxicity.
Storage and Handling
Storage: Store at room temperature, away from moisture and heat.
Stability: Stable when stored properly, check expiration date.