What is the recommended dosage of Amiodarone for a patient with a history of cardiac issues, such as atrial fibrillation or ventricular tachycardia?

Amiodarone Dosing for Cardiac Arrhythmias

For atrial fibrillation, start with an oral loading dose of 600-800 mg daily in divided doses until a total of 10 grams has been administered (typically 1-2 weeks), then reduce to a maintenance dose of 200 mg daily. 1, 2

For ventricular tachycardia or ventricular fibrillation, use a higher loading dose of 800-1600 mg daily in divided doses until 10 grams total is reached, followed by maintenance therapy of 200-400 mg daily. 1, 3

Loading Phase Strategy

Atrial Fibrillation

• Outpatient loading: 600-800 mg daily in divided doses (typically 400 mg twice daily or 200-300 mg three times daily) until 10 grams total accumulated dose 2
• Duration: Approximately 1-2 weeks depending on daily dose used 2
• Higher doses (up to 1200 mg daily) may be considered in monitored inpatient settings, though this increases adverse effect risk 1

Ventricular Arrhythmias

• Loading dose: 800-1600 mg daily in divided doses until 10 grams total 1, 3
• This higher loading is necessary for life-threatening ventricular arrhythmias compared to atrial fibrillation 1
• The American Heart Association specifically recommends this aggressive approach for ventricular arrhythmias 3

Maintenance Dosing

Standard Maintenance

• Atrial fibrillation: 200 mg daily after completing 10-gram load 2
• Ventricular arrhythmias: 200-400 mg daily after completing 10-gram load 1, 3
• The lowest effective dose should always be used, as adverse effects are dose-related and occur in 35-51% of patients 2

Dose Reduction for Adverse Effects

• If bradycardia develops, reduce to 200 mg every 24 hours rather than discontinuing 2
• Low-dose amiodarone (200 mg daily or less) can be effective with fewer side effects 2
• Virtually all patients develop side effects at maintenance doses of 600 mg daily, so lower doses are preferable 1

Intravenous Administration (Acute Settings)

Initial IV Dosing

• Loading: 150 mg IV bolus over 10 minutes 2, 4
• Maintenance infusion: 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours 2, 4
• Total first 24 hours: Approximately 1000 mg 4
• The FDA label specifies that mean daily IV doses above 2100 mg are associated with increased hypotension risk 4

Breakthrough Arrhythmias on IV

• Supplemental bolus: 150 mg in 100 mL D5W over 10 minutes for breakthrough VF or hemodynamically unstable VT 4
• The maintenance infusion rate may be increased to achieve effective suppression 4

Transitioning from IV to Oral Therapy

Duration-Based Conversion Protocol

This is critical because patients on IV therapy have already accumulated significant tissue stores 1:

• Less than 1 week of IV: Start 800-1600 mg oral daily 1, 3
• 1-3 weeks of IV: Start 600-800 mg oral daily 1, 3
• More than 3 weeks of IV: Start 400 mg oral daily 1, 3

Transition Strategy

• Begin oral dosing while IV infusion continues at 0.5 mg/min 3
• This overlap accounts for amiodarone's extremely long half-life (up to 100 days) 3
• Continue oral loading until 10 grams total oral dose is achieved, then reduce to maintenance 3

Critical Monitoring Requirements

During Loading Phase

• ECG monitoring: Watch for bradycardia, QT prolongation, hypotension, and heart block 1
• Heart rate: Check every 4-6 hours initially, then at least daily 3
• Continuous telemetry: For at least 24 hours after IV discontinuation 3
• Daily ECG: To assess QT interval and detect heart block 3

Drug Interactions Requiring Immediate Dose Adjustment

• Digoxin: Reduce dose by 50% immediately, as amiodarone doubles digoxin levels 3
• Warfarin: Reduce dose by 30-50% and check INR within 3-5 days, as amiodarone significantly increases INR 1, 3
• Other rate-control agents: Reduce doses of beta-blockers and calcium channel blockers as amiodarone's rate-control effect develops 3

Long-Term Monitoring

• Thyroid function: Regular monitoring essential 2
• Liver function: Monitor for hepatotoxicity 2
• Pulmonary function: Watch for pulmonary toxicity (occurs in approximately 5% of patients) 2
• Ophthalmologic: Corneal microdeposits occur in virtually all patients but are rarely clinically significant 5

Common Pitfalls and Caveats

Onset of Action

• Full antiarrhythmic effect takes days to weeks despite adequate serum levels 1
• The pretherapeutic latency period varies by arrhythmia type and dose used 6
• Maximal effects may not occur until 90-150 days of treatment 6

Adverse Effects

• Cardiovascular: Bradycardia (1-3% oral, 4.9% IV), hypotension (16% with IV), AV block 2, 3
• Gastrointestinal: Nausea, constipation, anorexia (common) 2
• Pulmonary toxicity: Serious but occurs in only 5% of patients 2
• Thyroid dysfunction: Occurs in approximately 6% of patients 2
• Neurologic: Tremor and ataxia are common (35% in some studies) 7

Administration Considerations

• Concentrations >2 mg/mL require central venous catheter 4
• Use volumetric infusion pump, not drop counters (can result in 30% underdosing) 4
• Administer through in-line filter 4
• Use glass or polyolefin bottles for infusions >2 hours 4

Special Clinical Scenarios

• Heart failure patients: Amiodarone is safe in severe heart failure and myocardial damage, unlike many other antiarrhythmics 8
• Relatively asymptomatic AF: Aggressive rhythm control with amiodarone does not improve outcomes; reserve for highly symptomatic patients when rate control with anticoagulation is inadequate 2
• Post-cardioversion: After successful cardioversion, continue with standard loading protocol (10-gram total) then maintenance 3

Persistence After Discontinuation

• Antiarrhythmic protection may persist for 150 days or more after discontinuation due to the extremely long half-life 6
• This provides continuous control but also means adverse effects may persist long after stopping the drug 6