What is the recommended infusion protocol for amiodarone in an adult patient with life-threatening arrhythmias, considering potential pre-existing conditions such as liver disease or pulmonary fibrosis?

Amiodarone Infusion Protocol for Life-Threatening Arrhythmias

For adult patients with life-threatening ventricular arrhythmias, administer amiodarone as a 150 mg IV bolus over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for the remaining 18 hours (total 1,050 mg over 24 hours). 1, 2, 3

Standard Infusion Protocol

Initial Loading Phase

• Rapid bolus: 150 mg IV diluted in 100 mL D5W over 10 minutes 1, 2, 3
• First maintenance: 1 mg/min infusion for 6 hours (360 mg total) 1, 2, 3
• Second maintenance: 0.5 mg/min for remaining 18 hours (540 mg total) 1, 2, 3
• Total 24-hour dose: Approximately 1,050 mg 1, 2

Breakthrough Arrhythmias

• For recurrent VF or hemodynamically unstable VT during infusion, repeat the 150 mg bolus over 10 minutes 1, 3
• An additional 150 mg bolus may be given if VF/VT persists after initial treatment 2
• Maximum total dose should not exceed 2.2 grams over 24 hours 2

Cardiac Arrest Protocol

• For VF/pulseless VT unresponsive to defibrillation: 300 mg IV/IO bolus over 10 minutes 1, 2
• Second dose: 150 mg IV/IO if rhythm persists 1, 2

Administration Requirements

Vascular Access

• Mandatory central line for concentrations >2 mg/mL 4, 2
• For infusions >1 hour, do not exceed 2 mg/mL concentration via peripheral line due to severe phlebitis risk (occurs frequently) 4, 2
• Use in-line filter during administration 4

Monitoring During Infusion

Continuous ECG monitoring is mandatory for: 4, 2

• Heart rate and rhythm
• AV conduction abnormalities
• QT interval prolongation
• Blood pressure (hypotension occurs in 16% of patients) 2

Pre-Existing Conditions: Critical Modifications

Absolute Contraindications (Do Not Administer)

• Second- or third-degree AV block without functioning pacemaker 1, 2, 3
• Marked sinus bradycardia without pacemaker 3
• Cardiogenic shock 3
• Known hypersensitivity to amiodarone or iodine 3

Liver Disease

• Use with extreme caution in hepatic dysfunction 1
• Amiodarone causes hepatic toxicity and transaminitis 5
• Monitor liver function tests closely during infusion 5
• No specific dose adjustment is provided in guidelines, but lower maintenance doses (100-200 mg daily oral) should be considered after IV loading 1

Pulmonary Fibrosis or Lung Disease

• Contraindicated in acute inflammatory lung disease 1
• Pre-existing pulmonary fibrosis is a relative contraindication - risk of worsening is directly related to cumulative dose and duration 6, 5
• Amiodarone causes pulmonary toxicity through phospholipid accumulation in type II pneumocytes 6
• Baseline chest X-ray and pulmonary function tests should have been obtained before initiating therapy 6
• In life-threatening situations, proceed with IV loading if no alternative exists, but transition to lowest effective oral maintenance dose 1, 6

Heart Failure and Hypotension

• Safe to use in severe left ventricular dysfunction - amiodarone was used safely in critically ill patients with impaired LV function 7
• If hypotension develops (16% incidence): slow infusion rate, add vasopressors, positive inotropes, or volume expansion as needed 1, 3
• Do not discontinue unless hypotension is refractory 3

Bradycardia Risk

• Baseline heart rate <60 bpm requires extreme caution 4
• Bradycardia occurs in 4.9% of IV amiodarone patients 4, 2
• If heart rate decreases by ≥10 bpm during infusion: reduce infusion rate immediately 4
• If second- or third-degree heart block develops: discontinue infusion unless pacemaker present 4, 3

Critical Drug Interactions During IV Infusion

Immediate Dose Adjustments Required

• Digoxin: Reduce dose by 50% when starting amiodarone (levels will double) 1, 4
• Warfarin: Reduce dose by 33-50% and monitor INR at least weekly (interaction peaks at 7 weeks) 1, 4
• Avoid concomitant QT-prolonging drugs without expert consultation 1, 4

Additive Bradycardia Risk

• Concomitant beta-blockers, calcium channel blockers, or digoxin create additive AV nodal blockade 4
• Consider holding or reducing doses of these agents during IV loading if bradycardia develops 4

Transition to Oral Therapy

Duration-Based Conversion

• IV <1 week: Transition to 800-1,600 mg oral daily 8
• IV 1-3 weeks: Transition to 600-800 mg oral daily 8
• IV >3 weeks: Transition to 400 mg oral daily 8
• Significant tissue stores accumulate during IV therapy, allowing lower oral doses 8

Common Pitfalls to Avoid

1. Do not use peripheral IV for prolonged infusions - phlebitis is nearly universal with concentrations >2 mg/mL 4, 2
2. Do not combine with other antiarrhythmic agents - proarrhythmic risk increases substantially 1
3. Do not ignore new bradycardia - this signals excessive AV nodal suppression requiring immediate rate reduction 4
4. Do not forget drug interactions - digoxin and warfarin toxicity are predictable and preventable 1, 4
5. Do not exceed 2.2 grams in 24 hours - higher doses increase toxicity without additional efficacy 2