What is the typical dosage regimen for Amiodarone (antiarrhythmic medication) in treating arrhythmias?

Amiodarone Dosage Regimen

For life-threatening ventricular arrhythmias, initiate IV amiodarone with a 150 mg bolus over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours; for oral therapy, load with 800-1,600 mg/day in divided doses until 10 grams total is administered, then maintain at 200-400 mg/day. 1, 2

Intravenous Dosing for Acute Life-Threatening Arrhythmias

Initial Loading Protocol

• Administer 150 mg IV bolus over 10 minutes for ventricular fibrillation/pulseless ventricular tachycardia unresponsive to defibrillation 1, 3, 2
• If VF/pulseless VT persists, give a second 150 mg bolus 3
• For cardiac arrest with refractory VF/pulseless VT, the American College of Cardiology recommends 300 mg IV bolus when rhythm remains unresponsive to CPR, defibrillation, and epinephrine 3

Maintenance Infusion

• After initial bolus, infuse 1 mg/min for 6 hours 1, 2
• Then reduce to 0.5 mg/min for 18 hours (total 720 mg/24 hours) 1, 2
• Continue maintenance infusion at 0.5 mg/min for up to 2-3 weeks 2
• Total first 24-hour dose should approximate 1000 mg 2

Breakthrough Arrhythmias During IV Therapy

• For breakthrough VF or hemodynamically unstable VT, administer 150 mg supplemental infusion in 100 mL D5W over 10 minutes 2
• The maintenance infusion rate may be increased to achieve effective arrhythmia suppression 2
• Mean daily doses above 2100 mg are associated with increased risk of hypotension 2

Critical Administration Details

• Use concentrations ≤2 mg/mL for peripheral IV to minimize phlebitis risk 2
• Concentrations >2 mg/mL require central venous catheter 2
• Must use volumetric infusion pump (not drop counters, which can underdose by 30%) 2
• Administer through dedicated central line with in-line filter whenever possible 2

Oral Dosing Regimens

Ventricular Arrhythmias

• Loading: 800-1,600 mg/day in divided doses until 10 grams total administered 1, 4, 3
• Maintenance: 200-400 mg/day after loading complete 1, 4, 3
• Alternative loading: 600 mg twice daily for 7 days, then 600 mg daily 5
• High-dose rapid loading (for unstable patients): 50 mg/kg/day for 3 days, then 30 mg/kg/day for 2 days, followed by 300-400 mg twice daily 6

Atrial Fibrillation

• Loading: 600-800 mg/day in divided doses until 10 grams total administered 1, 4
• Maintenance: 200 mg/day 1, 4
• May use higher initial dosing or IV loading in unstable inpatients 1

Supraventricular Tachycardias

• Lower maintenance doses of 100-400 mg/day are typically sufficient 7
• Most patients with recurrent SVT or atrial fibrillation achieve control with these smaller doses 7

Transitioning from IV to Oral Therapy

Conversion Dosing Based on IV Duration

• <1 week IV therapy: 800-1,600 mg oral daily 1, 4
• 1-3 weeks IV therapy: 600-800 mg oral daily 1, 4
• >3 weeks IV therapy: 400 mg oral daily 1, 4

Monitoring During Transition

• Monitor closely for breakthrough arrhythmias in first 6 hours after IV discontinuation 3
• Watch for bradycardia, QT prolongation, and heart block 1, 4
• Monitor blood pressure for hypotension 4
• Full antiarrhythmic effect may take days to weeks despite adequate serum levels 4

Dose Adjustment Principles

Maintenance Dose Reduction

• Most patients require dose reduction from initial loading due to side effects 5
• In one study, doses decreased from 572±283 mg/day at 45 days to 372±174 mg/day at 6 months 5
• Start at relatively low maintenance dose with upward titration as needed 1

Monitoring Parameters During Dose Titration

• PR interval (affected by flecainide, propafenone, sotalol, amiodarone) 1
• QRS duration (affected by flecainide, propafenone) 1
• QT interval (affected by sotalol, amiodarone, disopyramide) 1
• Reassess ECG with each dose change 1

Common Pitfalls and Safety Considerations

Cardiovascular Adverse Effects

• Hypotension occurs in 16% of IV patients 4
• Bradycardia and AV block occur in 4.9% of IV patients and 1-3% of oral patients 4
• QT prolongation is common but rarely causes torsades de pointes 1, 4

Non-Cardiac Toxicity

• 93% of patients develop side effects on standard dosing 5
• Virtually all patients develop corneal microdeposits 5
• Pulmonary toxicity occurs in approximately 5% of patients 8
• Gastrointestinal effects (especially constipation) are extremely common 1, 5
• Neurologic effects (tremor, ataxia) occur in up to 35% of patients 8

Critical Drug Interactions

• Warfarin clearance is reduced—expect sudden INR increases requiring dose adjustment 4
• Digoxin levels typically double with coadministration 4
• Amiodarone inhibits multiple cytochrome P450 pathways 4

Severe Toxicity Risk

• Loading infusions at concentrations and rates exceeding recommendations have resulted in hepatocellular necrosis, acute renal failure, and death 2
• 10-19% of patients must discontinue due to severe side effects 5, 8
• First sign of antiarrhythmic failure may be sudden cardiac death 5

Pharmacokinetic Considerations

Prolonged Half-Life Effects

• Elimination half-life is approximately 30 days (range 15-100 days) 7
• Pretherapeutic latency period varies by arrhythmia type and dose 7
• Maximal effects not attained before 90-150 days of treatment 7
• Antiarrhythmic protection may persist up to 150 days after discontinuation 7