Are there situations where the initial bolus dose of amiodarone should be withheld or modified?

When to Withhold the Initial Amiodarone Bolus

The initial bolus dose of IV amiodarone should be withheld in patients with marked sinus bradycardia, second- or third-degree AV block without a functioning pacemaker, or cardiogenic shock, as these are absolute contraindications. 1

Absolute Contraindications to IV Amiodarone Bolus

The FDA label clearly identifies situations where amiodarone must not be given 1:

• Marked sinus bradycardia - The drug causes bradycardia in 4.9% of patients even without pre-existing conduction disease 2, 1
• Second- or third-degree AV block unless a functioning pacemaker is in place 1, 3
• Cardiogenic shock 1
• Known hypersensitivity to amiodarone or iodine 1

Clinical Scenarios Requiring Extreme Caution

Pre-existing Bradycardia

In patients with baseline heart rates below 60 bpm without life-threatening arrhythmia, IV amiodarone should be used with extreme caution and is relatively contraindicated unless a pacemaker is available or the situation is immediately life-threatening with no safer alternatives. 2

• If the patient has a heart rate of 57 bpm and the arrhythmia is immediately life-threatening (VF/pulseless VT), proceed with the 150 mg bolus over 10 minutes while monitoring continuously 2
• If heart rate decreases by 10 beats per minute during infusion, reduce the infusion rate immediately 2
• Consider alternative agents (beta-blockers, calcium channel blockers) first if the clinical situation permits 2

Concomitant AV Nodal Blocking Agents

Patients already receiving beta-blockers, calcium channel blockers, or digoxin have additive bradycardic effects and require heightened vigilance. 2

• The risk of severe bradycardia or heart block increases substantially with concurrent use of these medications 2
• Continuous ECG monitoring is mandatory to detect second- or third-degree heart block, which represents an absolute contraindication to continued therapy 2

Cardiac Arrest Context: Different Rules Apply

In cardiac arrest with VF or pulseless VT unresponsive to defibrillation and epinephrine, give the 300 mg IV/IO bolus regardless of baseline rhythm, as the patient is already in extremis. 4

• The American Heart Association guidelines support amiodarone for refractory VF/pulseless VT after failed defibrillation, CPR, and vasopressor therapy 4
• A second 150 mg bolus may be given if the rhythm persists 4
• In this setting, the immediate mortality risk of untreated VF/VT far outweighs concerns about bradycardia or hypotension 4

Hemodynamic Instability Considerations

Hypotension occurs in 16% of patients receiving IV amiodarone, so the bolus should be given cautiously in patients with borderline blood pressure. 2, 1

• A canine study demonstrated that administering a vasoconstrictor before amiodarone prevented hypotension 4
• If hypotension develops during the bolus, slow the infusion rate and consider vasopressors, positive inotropic agents, or volume expansion 1
• The adverse hemodynamic effects are attributed to vasoactive solvents (polysorbate 80 and benzyl alcohol) in the IV formulation 4

Administration Safety Requirements

When the bolus is appropriate, specific precautions minimize risk 1:

• Use a central venous catheter whenever possible, especially for concentrations >2 mg/mL 1
• Use an in-line filter during administration 1
• Administer via volumetric infusion pump, never drop counters (which can underdose by up to 30%) 1
• Mix in glass or polyolefin bottles with D5W for infusions exceeding 2 hours 1

Common Pitfall to Avoid

Do not confuse the cardiac arrest bolus dose (300 mg) with the non-arrest bolus dose (150 mg). 4, 3

• For life-threatening ventricular arrhythmias in a perfusing patient: 150 mg over 10 minutes 3, 1
• For cardiac arrest VF/pulseless VT: 300 mg IV/IO bolus 4, 3
• Supplemental 150 mg boluses may be given for breakthrough arrhythmias in either scenario 3, 1