What is the recommended dose of digoxin (digitalis glycoside) in a patient receiving an amiodarone (antiarrhythmic medication) infusion?

Digoxin Dosing During Amiodarone Infusion

When administering digoxin to a patient on amiodarone infusion, the digoxin dose should be reduced by 30-50% from the standard dose due to the significant drug interaction that increases digoxin levels. 1

Mechanism of Interaction

• Amiodarone inhibits P-glycoprotein, which reduces digoxin clearance and increases serum digoxin concentrations 1
• This interaction causes digoxin levels to predictably double after coadministration with amiodarone 1, 2
• The interaction occurs through multiple mechanisms, including decreased renal tubular secretion of digoxin 1, 2
• Amiodarone increases oral bioavailability of digoxin and reduces total body clearance by approximately 29% 2, 3

Specific Dosing Recommendations

• For IV digoxin loading during amiodarone infusion:

  • Standard loading dose: 0.25-0.5 mg IV bolus 1
  • Adjusted loading dose with amiodarone: Reduce by 30-50% to approximately 0.125-0.35 mg IV bolus 1
  • Maximum 24-hour loading dose should be reduced proportionally from the standard 1.0 mg over 24 hours 1

• For maintenance dosing:

  • Standard maintenance: Based on patient's age, weight, renal function (typically 0.125-0.25 mg daily) 1
  • Adjusted maintenance with amiodarone: Reduce by 30-50% from calculated dose 1

Monitoring Requirements

• Check digoxin levels more frequently when initiating or adjusting amiodarone therapy 1, 4
• Target trough serum digoxin level: 0.5-1.0 ng/mL (lower than the standard 0.8-2.0 ng/mL range) 1
• Monitor for signs of digoxin toxicity:
  • Gastrointestinal symptoms: anorexia, nausea, vomiting 1, 5
  • Neurological symptoms: visual disturbances, confusion 1, 5
  • Cardiac arrhythmias: bradycardia, heart block, various tachyarrhythmias 1, 5

Clinical Considerations

• The peak effect of this interaction may take several weeks to fully develop, requiring ongoing monitoring and potential dose adjustments 1, 4
• Digoxin levels may fluctuate significantly based on the timing of blood sampling in relation to amiodarone administration 4
• Blood samples for digoxin levels are best drawn at least 6-8 hours after the last digoxin dose 4
• Tissue concentrations of digoxin may not correlate well with plasma concentrations in this setting 4

Precautions

• Use with extreme caution in patients with:
  • Renal dysfunction (further reduces digoxin clearance) 1
  • Pre-existing AV block or SA node dysfunction 1
  • Wolff-Parkinson-White syndrome with atrial fibrillation/flutter 1
• Avoid this combination in patients with second or third-degree heart block without a pacemaker 1
• Consider alternative rate control strategies in patients with multiple risk factors for digoxin toxicity 6