Cardiac Glycoside Management

Introduction to Cardiac Glycosides

• The American College of Cardiology and the American Heart Association recommend digoxin as a cardiac glycoside for patients with symptomatic heart failure and left ventricular ejection fraction (LVEF) <40% to improve ventricular function, patient well-being, and reduce hospitalizations due to worsening heart failure, with a Class IIa recommendation 1, 2
• Digoxin is especially useful for controlling ventricular rate in patients with atrial fibrillation, particularly when the resting heart rate is >80 beats per minute (bpm) or during exercise >110-120 bpm, as recommended by the European Society of Cardiology 2
• The American College of Cardiology/American Heart Association has downgraded cardiac glycosides from Class I to Class IIa recommendation due to narrow risk/benefit ratio 1

Diagnosis and Treatment of Digoxin Toxicity

• Characteristic arrhythmia, such as bidirectional or fascicular ventricular tachycardia, is highly suggestive of digoxin toxicity, according to the American College of Cardiology 3
• Serum digoxin concentration levels >2.0 ng/mL are often associated with toxicity, and levels >4.0 ng/mL indicate severe toxicity requiring immediate treatment, as stated by the American College of Cardiology 3
• Discontinue digoxin in all cases of suspected toxicity, as recommended by the American College of Cardiology 3
• Administer digoxin-specific antibody fragments (digoxin-Fab) for life-threatening arrhythmias, hemodynamic instability, serum digoxin concentration >4 ng/mL with serious arrhythmias, or severe hyperkalemia (>5.5 mEq/L) in acute toxicity, which is a Class I recommendation by the American Heart Association 4
• Correct electrolyte abnormalities by repleting potassium to ≥4.0 mmol/L and magnesium to normal values (≥2.0 mmol/L), as recommended by the American College of Cardiology 3

Management of Arrhythmias

• For bradyarrhythmias, atropine may be reasonable (Class IIb recommendation) and temporary pacing if unresponsive to medical therapy (Class IIb recommendation), according to the American Heart Association 4
• For ventricular arrhythmias, lidocaine, phenytoin, or bretylium may be reasonable until digoxin-Fab can be administered (Class IIb recommendation), as stated by the American Heart Association 4
• For torsades de pointes, IV magnesium sulfate and temporary pacing or isoproterenol to increase heart rate are recommended, according to the American College of Cardiology 3

Monitoring and Follow-up

• Continue cardiac monitoring for 24-48 hours after digoxin-Fab administration, and monitor for rebound toxicity (rare but possible) 4
• Serum digoxin levels become unreliable after digoxin-Fab administration, as stated by the American College of Cardiology 3
• Target a lower therapeutic range (0.6-1.2 ng/mL) for digoxin therapy, as recommended by the European Society of Cardiology 2

Dosage and Administration

• The recommended dosage for adults with normal renal function is 0.25 mg/day, and for elderly patients (>70 years), the recommended dosage is 0.125-0.0625 mg/day, as recommended by the European Society of Cardiology and the American Heart Association 2, 5
• Generally, no loading doses are required in stable patients with sinus rhythm, but the American Heart Association recommends a total loading dose of 8-12 mcg/kg for the initial loading phase of digoxin therapy in patients with heart failure or atrial fibrillation 2, 6, 7
• The therapeutic range is 0.6-1.2 ng/ml, and routine measurement of serum levels is not necessary in most patients, as recommended by the European Society of Cardiology 2
• Patients with renal failure require special attention, with the recommended digoxin dose based on renal function as follows:

Contraindications and Interactions

• Digoxin is contraindicated in patients with second or third-degree heart block without a pacemaker, pre-excitation syndromes, or previous evidence of digoxin intolerance, as stated by the European Society of Cardiology and the American Heart Association 2, 12, 13, 8, 10, 14
• Concomitant use of medications that increase serum digoxin levels (amiodarone, verapamil, diltiazem, certain antibiotics, quinidine) should be avoided, and the dose of digoxin should be reduced by 30-50% when coadministered with verapamil, clarithromycin, erythromycin, itraconazole, or amiodarone, as recommended by the American Heart Association 2, 5, 15
• The American College of Cardiology recommends reducing digoxin dose by at least 50% when co-administered with dronedarone, due to increased risk of toxicity 8

Efficacy and Safety

• Digoxin reduces heart failure hospitalizations but does not reduce mortality, according to the American College of Cardiology, in patients with heart failure or atrial fibrillation 1, 15
• Digoxin is more effective when combined with beta-blockers for rate control, particularly during exercise, in patients with atrial fibrillation, and improves symptoms, quality of life, and exercise tolerance, and reduces hospitalizations due to heart failure, but does not reduce overall mortality, in patients with heart failure or atrial fibrillation 1, 15, 16, 11
• Digoxin can be beneficial to decrease heart failure hospitalizations (Class IIa recommendation) and is most effective when added to patients with persistent symptoms despite guideline-directed medical therapy (GDMT) 11

Management of Side Effects

• For patients taking digoxin who experience constipation, the American Gastroenterological Association recommends polyethylene glycol (PEG) as the first-line treatment, with fiber supplements as an appropriate initial option for mild cases, and increase fluid intake, particularly in patients with low fluid intake, is recommended to help manage constipation in patients taking digoxin 17, 18
• Peripherally acting μ-opioid receptor antagonists (methylnaltrexone, naloxegol) can be considered for opioid-induced constipation in patients taking digoxin, as suggested by the National Comprehensive Cancer Network 19